Blood pressure monitor

ABSTRACT

A blood pressure monitor including a cuff, a pressure sensor which detects a pressure in the cuff, a pressure regulating device which increases the pressure of the cuff, a pulse-amplitude determining device for determining an amplitude of each of pulses of a pulse wave which are produced in the cuff and detected by the pressure sensor while the cuff pressure is increased, a candidate determining device for determining, as a diastolic BP candidate, a pressure of the cuff which is detected by the pressure sensor and which corresponds to an amplitude of a first pulse of the pulses determined by the pulse-amplitude determining device, by judging whether the amplitude of the first pulse is not greater than a reference value which is smaller than an amplitude of at least one second pulse of the pulses, by a predetermined proportion of the amplitude of the second pulse, the amplitude of the second pulse being determined by the pulse-amplitude determining device after the amplitude of the first pulse is determined, and a BP determining device for determining, as a monitor diastolic BP value, the cuff pressure corresponding to the amplitude of the first pulse, when the candidate determining device determines, as the diastolic BP candidate, the cuff pressure corresponding to the amplitude of the first pulse, with respect to a predetermined number of the one or more second pulses.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a blood pressure monitorincluding an inflatable cuff.

[0003] 2. Related Art Statement

[0004] There is known a blood pressure (BP) monitor which includes aninflatable cuff adapted to be wound around a body portion, e.g., upperarm, of a living subject, e.g., patient, to press the body portion. TheBP monitor functions as an automatic BP measuring device whichperiodically measures a BP value of the subject by increasing the cuffpressure and thereby pressing the body portion of the subject. However,if the period or interval of the BP measurements effected by the BPmonitor is shortened for improving the accuracy of monitoring ofsubject's blood pressure, the frequency of pressing of subject's bodyportion is increased, which causes the subject to feel discomfort.

[0005] In the above-indicated background, it has been proposed toincrease the pressure of an inflatable cuff being wound around a bodyportion of a living subject, up to a predetermined value, detect a pulsewave that is a pressure oscillation produced in the cuff, and estimate aBP value of the subject based on the magnitude of the pulse wave. Thistechnique is disclosed in, e.g., Japanese Patent Application laid openfor inspection purposes under Publication No. 61(1986)-103432, orJapanese Patent Application laid open for inspection purposes underPublication No. 60(1985)-241422.

[0006] Regarding the above-indicated conventional BP monitor techniques,however, there are known some cases where it is difficult to detect achange of magnitudes of pulse waves which reflects a change of bloodpressure of a living subject, if BP values are estimated based on thepulse waves detected at a considerably low cuff pressure, whichcontributes to reducing the discomfort felt by the subject. Morespecifically described, respective amplitudes of pulses of a pulse wavewhich is detected from an inflatable cuff being wound around a bodyportion of a living subject whose blood pressure is normal, has anenvelope indicated at solid line in the graph of FIG. 6. In contrast,amplitudes of pulses of a pulse wave obtained from a living subjectwhose blood pressure is low, has an envelope indicated at one-dot chainline in FIG. 6. In the case where amplitudes of pulses of a pulse waveare detected at a considerably low cuff pressure, e.g., pressure, P_(K),in FIG. 6, an amount of change of the pulse amplitudes with respect toan amount of change of blood pressure of a living subject may be toosmall. Thus, when the BP monitor is used at the low cuff pressure P_(K),it may not be able to monitor the blood pressure of the subject withhigh accuracy.

[0007] There is also known a continuous BP monitor which includes aninflatable cuff which is adapted to be wound around a body portion of aliving subject to press the body portion; a blood pressure measuringdevice which measures a blood pressure of the subject by changing apressure in the cuff; a pressure pulse wave sensor which is adapted tobe pressed against a distal section of the artery located on a distalside of the cuff wound around the body portion, so as to detect apressure pulse wave which is produced from the distal section of theartery; a relationship determining means which determines a relationshipbetween blood pressure and magnitude of pressure pulse wave, based onthe blood pressure measured by the blood pressure measuring device and amagnitude of the pressure pulse wave detected by the pressure pulse wavesensor; a blood pressure determining means which successively determinesa blood pressure of the subject according to the determined relationshipbased on a magnitude of each of successive heartbeat-synchronous pulsesof the pressure pulse wave detected by the pressure pulse wave sensor;and a display which displays the blood pressure values determined by theblood pressure determining means. This BP monitor is disclosed in, e.g.,Japanese Patent Application laid open for inspection purposes underPublication No. 1(1989)-214338 or Japanese Utility Model Applicationlaid open for inspection purposes under Publication No. 2(1990)-82309.

[0008] In the prior continuous BP monitor, the condition under which thepressure pulse wave sensor is pressed against subject's artery may bechanged due to, e.g., a physical motion of the subject. Hence, in orderto improve the accuracy of BP values determined by the BP determiningmeans, the relationship between blood pressure and magnitude of pressurepulse wave is updated at a predetermined period. However, the updatingof the relationship needs a blood pressure measurement of the bloodpressure measuring device including the inflation of the cuff. Inaddition, since the pressure pulse wave sensor is set on the distal sideof the cuff, the continuous BP determination of the BP determining meansis interrupted by the inflation of the cuff. This problem is exaggeratedif the period of updating of the relationship is shortened for improvingthe accuracy of the continuous BP monitoring.

SUMMARY OF THE INVENTION

[0009] It is a first object of the present invention to provide a bloodpressure monitor which includes an inflatable cuff and which monitorswith high accuracy the blood pressure of a living subject withoutcausing the subject to feel discomfort.

[0010] It is a second object of the present invention to provide acontinuous blood pressure monitor which includes an inflatable cuff andwhich continuously monitors the blood pressure of a living subject withreduced discomfort felt by the subject and with reduced interruptionfrequency.

[0011] The first object may be achieved according to a first aspect ofthe present invention, which provides a blood pressure monitor includingan inflatable cuff which is adapted to be wound around a body portion ofa living subject to press the body portion, a pressure sensor whichdetects a pressure in the cuff, a cuff-pressure regulating device whichincreases the pressure of the cuff, pulse-amplitude determining meansfor determining an amplitude of each of pulses of a pulse wave which areproduced in the cuff and detected by the pressure sensor while thepressure of the cuff is increased by the cuff-pressure regulatingdevice, candidate determining means for determining, as a diastolicblood pressure candidate, a pressure of the cuff which is detected bythe pressure sensor and which corresponds to an amplitude of a firstpulse of the pulses determined by the pulse-amplitude determining means,by judging whether the amplitude of the first pulse is not greater thana reference value which is smaller than an amplitude of at least onesecond pulse of the pulses, by a predetermined proportion of theamplitude of the second pulse, the amplitude of the second pulse beingdetermined by the pulse-amplitude determining means after the amplitudeof the first pulse is determined, and blood-pressure determining meansfor determining, as a monitor diastolic blood pressure value, thepressure of the cuff corresponding to the amplitude of the first pulse,when the candidate determining means determines, as the diastolic bloodpressure candidate, the pressure of the cuff corresponding to theamplitude of the first pulse, with respect to a predetermined number ofthe at least one second pulse.

[0012] In the blood pressure (BP) monitor in accordance with the firstaspect of the invention, the predetermined number may be one, two, or agreater number. For example, the predetermined number is three. Thus,the present BP monitor may determine a monitor diastolic BP value of aliving subject at a pressure level which is higher than the diastolic BPvalue and which corresponds to the “third” one of the subsequent pulsesdetermined after the initial pulse. The thus determined monitordiastolic BP value enjoys high accuracy. In addition, since the pressurelevel where the monitor diastolic BP value is determined is considerablylow, the subject does not feel discomfort.

[0013] According to a preferred feature of the first aspect of theinvention, the candidate determining means comprises judging means forjudging whether the amplitude of the first pulse is not greater than areference value which is smaller than an amplitude of each of aplurality of second pulses of the pulses, by a predetermined proportionof the amplitude of the each second pulse, the respective amplitudes ofthe second pulses being determined by the pulse-amplitude determiningmeans after the amplitude of the first pulse is determined.

[0014] According to another feature of the first aspect of theinvention, the cuff-pressure regulating device comprises pressureincreasing means for stepwise increasing the pressure of the cuff byalternately increasing the cuff pressure and maintaining the cuffpressure at each of a plurality of different pressure values, and thepulse-amplitude determining means determines an amplitude of at leastone pulse which is produced in the cuff and detected by the pressuresensor while the cuff pressure is maintained at the each pressure value.The pressure increasing means may increase the cuff pressure by aconstant pressure increase amount, for each time or step, or mayincrease the cuff pressure by an increase amount which is variabledepending upon the current cuff pressure. The pulse-amplitudedetermining means may determine an amplitude of a single pulse detectedby the pressure sensor while the cuff pressure is maintained at eachpressure value, or an average of respective amplitudes of two or morepulses detected while the cuff pressure is maintained at each pressurevalue. The thus determined pulse amplitude or amplitudes enjoy highaccuracy because they are free from adverse influences resulting fromthe increasing of the cuff pressure. Therefore, the monitor diastolic BPvalues of the subject are determined with accuracy based on the pulseamplitudes.

[0015] According to another feature of the first aspect of theinvention, the blood-pressure determining means comprises monitor meansfor iteratively determining the monitor diastolic blood pressure value.The monitor means may periodically determine the monitor diastolic bloodpressure value at a predetermined period or interval of time (i.e.,monitor cycle time).

[0016] According to another feature of the first aspect of theinvention, the BP monitor further comprises abnormality identifyingmeans for identifying an abnormality of the monitor diastolic bloodpressure values iteratively determined by the monitor means.

[0017] According to another feature of the first aspect of theinvention, the abnormality identifying means comprises means foridentifying the abnormality based on at least one of an amount of changeof a last determined value of the monitor diastolic blood pressurevalues from an average of the monitor diastolic blood pressure values,and a rate of change of the last determined value of the monitordiastolic blood pressure values from the average of the monitordiastolic blood pressure values.

[0018] According to another feature of the first aspect of theinvention, the BP monitor further comprising a blood pressure measuringdevice which increases the pressure of the cuff up to a target pressurewhich is higher than a systolic blood pressure of the subject andmeasures at least one of a systolic, a mean, and a diastolic bloodpressure value of the living subject based on a variation of respectiveamplitudes of pulses of a pulse wave which are produced in the cuff anddetected by the pressure sensor during at least one of the increasing ofthe cuff pressure up to the target pressure and a decreasing of the cuffpressure down from the target pressure. The target pressure may be,e.g., about 180 mmHg that is estimated to be sufficiently higher than anormal systolic BP value of a human being.

[0019] According to another feature of the first aspect of theinvention, the blood pressure measuring device comprises means formeasuring the at least one of the systolic, the mean, and the diastolicblood pressure value of the living subject when the abnormalityidentifying means identifies the abnormality.

[0020] According to another feature of the first aspect of theinvention, the BP monitor further comprising a display which displaysthe monitor diastolic blood pressure value determined by theblood-pressure determining means.

[0021] The second object may be achieved according to a second aspect ofthe present invention, which provides a blood pressure monitorcomprising an inflatable cuff which is adapted to be wound around a bodyportion of a living subject to press the body portion through which anartery of the subject extends; a blood pressure measuring device whichmeasures a blood pressure of the subject by changing a pressure in thecuff; a pressure pulse wave sensor which is adapted to be pressedagainst a distal section of the artery located on a distal side of thecuff wound around the body portion, so as to detect a pressure pulsewave which is produced from the distal section of the artery and ispropagated thereto via a skin tissue above the distal section;relationship determining means for determining a relationship betweenblood pressure and magnitude of pressure pulse wave, based on the bloodpressure measured by the blood pressure measuring device and a magnitudeof the pressure pulse wave detected by the pressure pulse wave sensor;blood pressure determining means for successively determining at least adiastolic blood pressure of the subject according to the determinedrelationship based on a magnitude of a lower-peak point of each ofsuccessive first heartbeat-synchronous pulses of the pressure pulse wavedetected by the pressure pulse wave sensor; cuff-pressure increasingmeans for increasing the pressure of the cuff at a predetermined rate;waveform-characteristic determining means for determining acharacteristic of a lower-peak portion of a waveform of each ofsuccessive second heartbeat-synchronous pulses of the pressure pulsewave which are detected by the pressure pulse wave sensor when thepressure of the cuff is increased at the predetermined rate by thecuff-pressure increasing means, the lower-peak portion including alower-peak point of the each second heartbeat-synchronous pulse; andjudging means for judging whether the determined relationship isaccurate, based on at least one diastolic blood pressure determined bythe blood pressure determining means and a pressure of the cuffcorresponding to a time when the waveform characteristics determined bythe waveform-characteristic determining means significantly largelychange.

[0022] In the blood pressure monitor in accordance with the secondaspect of the invention, if the judging means makes a positive judgment,the relationship need not be updated. Accordingly, the blood pressuremeasuring device does not inflate the cuff, and the subject is preventedfrom being pressed by the cuff. In addition, although the pressure pulsewave sensor is set on the distal side of the cuff, the blood pressuredetermining means can continue to successively determine blood pressurevalues according to the relationship based on the pressure pulse wavedetected by the pressure pulse wave sensor.

[0023] The second object may be achieved according to a third aspect ofthe present invention, which provides a blood pressure monitorcomprising an inflatable cuff which is adapted to be wound around a bodyportion of a living subject to press the body portion through which anartery of the subject extends; a blood pressure measuring device whichmeasures a blood pressure of the subject by changing a pressure in thecuff; a pressure pulse wave sensor which is adapted to be pressedagainst a distal section of the artery located on a distal side of thecuff wound around the body portion, so as to detect a pressure pulsewave which is produced from the distal section of the artery and ispropagated thereto via a skin tissue above the distal section;relationship determining means for determining a relationship betweenblood pressure and magnitude of pressure pulse wave, based on the bloodpressure measured by the blood pressure measuring device and a magnitudeof the pressure pulse wave detected by the pressure pulse wave sensor;blood pressure determining means for determining at least a diastolicblood pressure of the subject according to the determined relationshipbased on a magnitude of a lower-peak point of each of successive firstheartbeat-synchronous pulses of the pressure pulse wave detected by thepressure pulse wave sensor; cuff-pressure increasing means forincreasing the pressure of the cuff at a predetermined rate; a cuffpulse wave sensor which detects a cuff pulse wave which is a pressureoscillation produced in the cuff; phase-difference determining means fordetermining a phase difference of respective lower-peak points of eachof successive second heartbeat-synchronous pulses of the pressure pulsewave and a corresponding one of successive heartbeat-synchronous pulsesof the cuff pulse wave, the second heartbeat-synchronous pulses of thepressure pulse wave and the heartbeat-synchronous pulses of the cuffpulse wave being detected by the pressure pulse wave sensor and the cuffpulse wave sensor, respectively, when the pressure of the cuff isincreased at the predetermined rate by the cuff-pressure increasingmeans; and judging means for judging whether the determined relationshipis accurate, based on at least one diastolic blood pressure determinedby the blood pressure determining means and a pressure of the cuffcorresponding to a time when the phase differences determined by thephase-difference determining means significantly largely change.

[0024] In the blood pressure monitor in accordance with the third aspectof the invention, if the judging means makes a positive judgment, therelationship need not be updated. Accordingly, the blood pressuremeasuring device does not inflate the cuff, and the subject is preventedfrom being pressed by the cuff. In addition, although the pressure pulsewave sensor is set on the distal side of the cuff, the blood pressuredetermining means can continue to successively determine blood pressurevalues according to the relationship based on the pressure pulse wavedetected by the pressure pulse wave sensor.

[0025] The second object may be achieved according to a fourth aspect ofthe present invention, which provides a blood pressure monitorcomprising an inflatable cuff which is adapted to be wound around a bodyportion of a living subject to press the body portion through which anartery of the subject extends; a blood pressure measuring device whichmeasures a blood pressure of the subject by changing a pressure in thecuff; a pressure pulse wave sensor which is adapted to be pressedagainst a distal section of the artery located on a distal side of thecuff wound around the body portion, so as to detect a pressure pulsewave which is produced from the distal section of the artery and ispropagated thereto via a skin tissue above the distal section;relationship determining means for determining a relationship betweenblood pressure and magnitude of pressure pulse wave, based on the bloodpressure measured by the blood pressure measuring device and a magnitudeof the pressure pulse wave detected by the pressure pulse wave sensor;blood pressure determining means for determining at least a mean bloodpressure of the subject according to the determined relationship basedon a mean magnitude of each of successive first heartbeat-synchronouspulses of the pressure pulse wave detected by the pressure pulse wavesensor; cuff-pressure increasing means for increasing the pressure ofthe cuff at a predetermined rate; pulse-area calculating means forcalculating an area defined by each of successive secondheartbeat-synchronous pulses of the pressure pulse wave which aredetected by the pressure pulse wave sensor when the pressure of the cuffis increased at the predetermined rate by the cuff-pressure increasingmeans; half-area identifying means for identifying that the pulse areascalculated by the pulse-area calculating means have decreased to half aninitial pulse area obtained before the cuff-pressure increasing meansstarts increasing the pressure of the cuff; and judging means forjudging whether the determined relationship is accurate, based on atleast one mean blood pressure determined by the blood pressuredetermining means and a pressure of the cuff corresponding to a timewhen the half-area identifying means identifies that the pulse areascalculated by the pulse-area calculating means have decreased to halfthe initial pulse area.

[0026] In the blood pressure monitor in accordance with the fourthaspect of the invention, if the judging means makes a positive judgment,the relationship need not be updated. Accordingly, the blood pressuremeasuring device does not inflate the cuff, and the subject is preventedfrom being pressed by the cuff. In addition, although the pressure pulsewave sensor is set on the distal side of the cuff, the blood pressuredetermining means can continue to successively determine blood pressurevalues according to the relationship based on the pressure pulse wavedetected by the pressure pulse wave sensor.

[0027] The second object may be achieved according to a fifth aspect ofthe present invention, which provides a blood pressure monitorcomprising an inflatable cuff which is adapted to be wound around a bodyportion of a living subject to press the body portion through which anartery of the subject extends; a blood pressure measuring device whichmeasures a blood pressure of the subject by changing a pressure in thecuff; a pressure pulse wave sensor which is adapted to be pressedagainst a distal section of the artery located on a distal side of thecuff wound around the body portion, so as to detect a pressure pulsewave which is produced from the distal section of the artery and ispropagated thereto via a skin tissue above the distal section;relationship determining means for determining a relationship betweenblood pressure and magnitude of pressure pulse wave, based on the bloodpressure measured by the blood pressure measuring device and a magnitudeof the pressure pulse wave detected by the pressure pulse wave sensor;blood pressure determining means for determining a blood pressure of thesubject according to the determined relationship based on a magnitude ofeach of successive first heartbeat-synchronous pulses of the pressurepulse wave detected by the pressure pulse wave sensor; cuff-pressureregulating means for increasing the pressure of the cuff up to apredetermined value and holding the cuff pressure at the predeterminedvalue; pulse-area calculating means for calculating an area defined byeach of successive second heartbeat-synchronous pulses of the pressurepulse wave which are detected by the pressure pulse wave sensor when thecuff pressure is held at the predetermined value by the cuff-pressureregulating means; and judging means for judging whether the determinedrelationship is accurate, based on a ratio of the calculated area of atleast one the second heartbeat-synchronous pulse of the pressure pulsewave detected by the pressure pulse wave when the cuff pressure is heldat the predetermined value by the cuff-pressure regulating means, to aninitial pulse area obtained before the cuff-pressure regulating meansstarts increasing the cuff pressure.

[0028] In the blood pressure monitor in accordance with the fifth aspectof the invention, if the judging means makes a positive judgment, therelationship need not be updated. Accordingly, the blood pressuremeasuring device does not inflate the cuff, and the subject is preventedfrom being pressed by the cuff. In addition, although the pressure pulsewave sensor is set on the distal side of the cuff, the blood pressuredetermining means can continue to successively determine blood pressurevalues according to the relationship based on the pressure pulse wavedetected by the pressure pulse wave sensor.

[0029] The first object may be achieved according to a sixth aspect ofthe present invention, which provides a blood pressure monitorcomprising an inflatable cuff which is adapted to be wound around a bodyportion of a living subject to press the body portion through which anartery of the subject extends; a blood pressure measuring device whichmeasures a blood pressure of the subject by changing a pressure in thecuff; a cuff pulse wave sensor which detects a cuff pulse wave which isa pressure oscillation produced in the cuff; a distal pulse wave sensorwhich detects a distal pulse wave from a distal section of the arterylocated on a distal side of the cuff wound around the body portion;cuff-pressure increasing means for increasing the pressure of the cuffat a predetermined rate; first peak-interval determining means fordetermining a first interval between an upper-peak point and alower-peak point of each of first heartbeat-synchronous pulses of thedistal pulse wave which are detected by the distal pulse wave sensorwhen the pressure of the cuff is increased at the predetermined rate bythe cuff-pressure increasing means; second peak-interval determiningmeans for determining a second interval between an upper-peak point anda lower-peak point of each of second heartbeat-synchronous pulses of thecuff pulse wave which are detected by the cuff pulse wave sensor whenthe pressure of the cuff is increased at the predetermined rate by thecuff-pressure increasing means; difference determining means fordetermining a difference between the first interval of the each of thefirst heartbeat-synchronous pulses and the second interval of acorresponding one of the second heartbeat-synchronous pulses; and bloodpressure determining means for determining, as a diastolic bloodpressure of the subject, a pressure of the cuff corresponding to a timewhen the differences determined by the difference determining meanssignificantly largely change.

[0030] In the blood pressure monitor in accordance with the sixth aspectof the invention, the upper-peak and lower-peak points of each pulse ofthe cuff pressure wave are not influenced by the increasing of the cuffpressure, whereas the upper-peak and lower-peak points of each pulse ofthe distal pulse wave are influenced by the increasing of the cuffpressure, because the distal pulse wave sensor is set on the distal sideof the cuff. Therefore, the peak-interval differences are influenced bythe increasing of the cuff pressure. The Inventors have found that thephase of the distal pulse wave has a certain relationship with that ofthe cuff pulse wave and that this relationship significantly largelychanges when the cuff pressure becomes equal to a diastolic pressure ofthe subject. Thus, a cuff pressure corresponding to the time when thepeak-interval differences significantly largely change, can bedetermined as a diastolic pressure of the subject. In the case where aphysiological change such as arrhythmia occurs to the heart of thepatient, respective waveforms of the cuff pulse wave and the distalpulse wave change in a similar manner, therefore the peak-intervaldifferences are not influenced by this change. Thus, the diastolic BPvalue of the subject can be determined with high accuracy. The distalpulse wave sensor may be provided by a sensor employed for a differentpurpose from monitoring the blood pressure of the subject. In this case,the total number of sensors which are worn on the subject is reduced ascompared with the case where an exclusive distal pulse wave sensor isemployed. Although the distal pulse wave sensor is worn at a positiondownstream of the cuff, a measurement using the distal pulse wavesensor, different from the blood pressure measurement, can be continuedwithout being interrupted due to the inflation of the cuff, because in aBP monitoring operation the cuff pressure is not increased to valueshigher than the diastolic pressure of the subject.

[0031] According to a preferred feature of the sixth aspect of theinvention, the distal pulse sensor comprises a pressure pulse wavesensor which is adapted to be pressed against the distal section of theartery via a skin tissue above the distal section, so as to detect apressure pulse wave which is produced from the distal section and ispropagated thereto via the skin tissue.

[0032] According to another feature of the sixth aspect of theinvention, the distal pulse senior comprises a photoelectric pulse wavesensor which emits a plurality of lights having different wavelengthstoward the distal section of the artery via a skin tissue above thedistal section, and detects a photoelectric pulse wave representingrespective intensities of the lights reflected from the distal sectionvia the skin tissue or transmitted through the body portion. Thephotoelectric pulse wave sensor may be employed for measuring aperipheral blood circulation or a blood oxygen saturation of a livingsubject. The manner of measurement of peripheral blood circulation isdisclosed in, e.g., Japanese Patent Application laid open for inspectionpurposes under Publication No. 5(1993)-115445, and the manner ofmeasurement of blood oxygen saturation is disclosed in, e.g., JapanesePatent Application laid open for inspection purposes under PublicationNo. 50(1975)-128387.

[0033] The second object may be achieved according to a seventh aspectof the present invention, which provides a blood pressure monitorcomprising an inflatable cuff which is adapted to be wound around a bodyportion of a living subject to press the body portion through which anartery of the subject extends; a blood pressure measuring device whichmeasures a blood pressure of the subject by changing a pressure in thecuff; a pressure pulse wave sensor which is adapted to be pressedagainst a distal section of the artery located on a distal side of thecuff wound around the body portion, so as to detect a pressure pulsewave which is produced from the distal section of the artery and ispropagated thereto via a skin tissue above the distal section;relationship determining means for determining a relationship betweenblood pressure and magnitude of pressure pulse wave, based on the bloodpressure measured by the blood pressure measuring device and a magnitudeof the pressure pulse wave detected by the pressure pulse wave sensor;blood pressure determining means for determining at least a diastolicblood pressure of the subject according to the determined relationshipbased on a magnitude of a lower-peak point of each of successive firstheartbeat-synchronous pulses of the pressure pulse wave detected by thepressure pulse wave sensor; cuff-pressure increasing means forincreasing the pressure of the cuff at a predetermined rate; a cuffpulse wave sensor which detects a cuff pulse wave which is a pressureoscillation produced in the cuff; first peak-interval determining meansfor determining a first interval between an upper-peak point and alower-peak point of each of first heartbeat-synchronous pulses of thedistal pulse wave which are detected by the distal pulse wave sensorwhen the pressure of the cuff is increased at the predetermined rate bythe cuff-pressure increasing means; second peak-interval determiningmeans for determining a second interval between an upper-peak point anda lower-peak point of each of second heartbeat-synchronous pulses of thecuff pulse wave which are detected by the cuff pulse wave sensor whenthe pressure of the cuff is increased at the predetermined rate by thecuff-pressure increasing means; difference determining means fordetermining a difference between the first interval of the each of thefirst heartbeat-synchronous pulses and the second interval of acorresponding one of the second heartbeat-synchronous pulses; andjudging means for judging whether the determined relationship isaccurate, based on at least one diastolic blood pressure determined bythe blood pressure determining means and a pressure of the cuffcorresponding to a time when the differences determined by thedifference determining means significantly largely change.

[0034] In the blood pressure monitor in accordance with the seventhaspect of the invention, if the judging means makes a positive judgment,the relationship need not be updated. Accordingly, the blood pressuremeasuring device does not inflate the cuff, and the subject is preventedfrom being pressed by the cuff. In addition, although the pressure pulsewave sensor is set on the distal side of the cuff, the blood pressuredetermining means can continue to successively determine blood pressurevalues according to the relationship based on the pressure pulse wavedetected by the pressure pulse wave sensor. Moreover, the accuracy ofthe relationship is judged by increasing the cuff pressure up to a valuearound the diastolic BP value of the patient, which does not cause thepatient to feel discomfort.

[0035] According to a preferred feature of the seventh aspect of theinvention, the blood pressure monitor further comprises a control devicewhich controls, when the judging means makes a negative judgment, theblood pressure measuring means to measure another blood pressure of thesubject, controls the pulse wave sensor to detect another magnitude ofthe pressure pulse wave sensor, and controls the relationshipdetermining means to determine another relationship between bloodpressure and magnitude of pressure pulse wave, based on the anotherblood pressure measured by the blood pressure measuring device and theanother magnitude of the pressure pulse wave detected by the pressurepulse wave sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and optional objects, features, and advantages of thepresent invention will better be understood by reading the followingdetailed description of the preferred embodiments of the invention whenconsidered in conjunction with the accompanying drawings, in which:

[0037]FIG. 1 is a diagrammatic view of a blood pressure (BP) monitorembodying the present invention;

[0038]FIG. 2 is an illustrative view for explaining various functions ofthe BP monitor of FIG. 1;

[0039]FIG. 3 is a flow chart representing a main routine which isexecuted by a control device of the BP monitor of FIG. 1;

[0040]FIG. 4 is a flow chart representing a BP monitor routine as a stepof the flow chart of FIG. 3;

[0041]FIG. 5A is a time chart showing a relationship between time andcuff pressure, P_(c), or pulse amplitude, A_(m);

[0042]FIG. 5B is a table showing a manner in which a cuff pressure,P_(c), is determined as a monitor diastolic blood pressure, MBP_(DIA);

[0043]FIG. 6 is a graph showing the envelope of pulse amplitudesobtained by changing cuff pressure applied to a living subject having anormal blood pressure, and the envelope of pulse amplitudes obtained bychanging cuff pressure applied to a living subject having a low bloodpressure;

[0044]FIG. 7 is a diagrammatic view of a continuous BP monitor as asecond embodiment of the present invention;

[0045]FIG. 8 is a graph showing an example of a pressure pulse wave(PPW) detected by a PPW sensor of the BP monitor of FIG. 7;

[0046]FIG. 9 is a graph showing a relationship determined by a controldevice of the BP monitor of FIG. 7;

[0047]FIG. 10 is an illustrative view for explaining various functionsof the control device of the BP monitor of FIG. 7;

[0048]FIG. 11 is a flow chart representing a control routine accordingto which the BP monitor of FIG. 7 operates;

[0049]FIG. 12 is a graph showing a relationship between waveformcharacteristic L and cuff pressure that is determined by the controldevice of the BP monitor of FIG. 7;

[0050]FIG. 13 is an illustrative view corresponding to FIG. 10, forexplaining various functions of a control device of a continuous BPmonitor as a third embodiment of the present invention;

[0051]FIG. 14 is a flow chart corresponding to FIG. 11, representing acontrol routine according to which the BP monitor of FIG. 13 operates;

[0052]FIG. 15 is a graph showing an example of a cuff pulse wave (CPW)detected by a CPW sensor, and an example of a pressure pulse wave (PPW)detected by a PPW sensor, of the BP monitor of FIG. 13;

[0053]FIG. 16 is a graph showing a relationship between phase differentT and cuff pressure that is determined by the control device of the BPmonitor of FIG. 13;

[0054]FIG. 17 is an illustrative view corresponding to FIG. 10, forexplaining various functions of a control device of a continuous BPmonitor as a fourth embodiment of the present invention;

[0055]FIG. 18 is a flow chart corresponding to FIG. 11, representing acontrol routine according to which the BP monitor of FIG. 17 operates;

[0056]FIG. 19 is an illustrative view corresponding to FIG. 10, forexplaining various functions of a control device of a continuous BPmonitor as a fifth embodiment of the present invention;

[0057]FIG. 20 is a flow chart corresponding to FIG. 11, representing acontrol routine according to which the BP monitor of FIG. 19 operates;

[0058]FIG. 21 is a cross-section view of a cuff pulse wave (CPW) sensoremployed by a continuous BP monitor as a sixth embodiment of the presentinvention;

[0059]FIG. 22 is an illustrative view corresponding to FIG. 10, forexplaining various functions of a control device of a continuous BPmonitor as a seventh embodiment of the present invention;

[0060]FIG. 23 is a graph showing an example of a cuff pulse wave (CPW)detected by a CPW sensor, and an example of a pressure pulse wave (PPW)detected by a PPW sensor, of the BP monitor of FIG. 22;

[0061]FIG. 24 is a flow chart corresponding to FIG. 11, representing acontrol routine according to which the BP monitor of FIG. 22 operates;

[0062]FIG. 25 is a graph showing a relationship between peak-intervaldifference t and cuff pressure that is determined by the control deviceof the BP monitor of FIG. 22;

[0063]FIG. 26 is a diagrammatic view corresponding to FIG. 7, showing apart of a BP monitor as an eighth embodiment of the present invention;

[0064]FIG. 27 is an illustrative view corresponding to FIG. 10, forexplaining various functions of a control device of the BP monitor ofFIG. 26; and

[0065]FIG. 28 is a flow chart representing a control routine accordingto which the BP monitor of FIG. 26 operates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Referring to FIGS. 1 through 4 and FIGS. 5A and 5B, there will bedescribed a blood pressure (BP) monitor to which the present inventionis applied.

[0067] In FIG. 1, reference numeral 10 designates an inflatable cuffwhich is adapted to be wound around an upper arm of a living subject,such as a patient. The cuff 10 is provided by an inflatable bag 10 aformed of a resilient sheet such as a rubber sheet or a vinyl sheet, anda non-stretchable arm belt 10 b in which the bag 10 a is accommodated.The bag 10 a is connected via air piping 18 to a pressure sensor 12, anair pump 14, and a pressure regulator valve 16.

[0068] The pressure sensor 12 includes a pressure-sensing semiconductorelement which detects an air pressure in the cuff 10 (i.e., bag 10 a),generates a pressure signal, SP, representing the detected cuffpressure, and supplies the pressure signal SP to each of a low-passfilter 20 and a band-pass filter 22. The low-pass filter 20 extracts,from the pressure signal SP, a direct-current (DC) componentrepresenting a static pressure, P_(c), of the cuff 10, and supplies acuff-pressure signal, SK, representing the static pressure P_(c), to ananalog-to-digital (A/D) converter 24. The band-pass filter 22 extracts,from the pressure signal SP, an alternate-current (AC) or frequency(e.g., 1 to 10 Hz) component representing pulses of a pulse wave whichare produced in the cuff 10. The band-pass filter 22 supplies apulse-wave signal, SM, representing the pulse wave, to the A/D converter24. The pulse wave is a pressure oscillation which is transmitted fromthe arteries (e.g., brachial artery) of the living subject to the cuff10 in synchronism with the heartbeat of the subject and is produced inthe cuff 10.

[0069] The band-pass filter 22 functions as a pulse-wave sensor, and hasa frequency characteristic that the band width thereof is sufficientlynarrow to be able to extract, freely from noise such as motion artifactnoise, the respective amplitudes of pulses of a pulse wave, i.e.,pressure oscillation that is produced in the cuff 10 in synchronism withthe heartbeat of the living subject, while the pressure of the cuff 10is slowly decreased at the rate of 2 to 3 mmHg/sec. The A/D converter 24includes a multiplexer which processes the two input signals SK, SM bytime sharing, and has the function of concurrently converting the twoanalog signals into digital signals SK, SM, which are supplied to acentral processing unit (CPU) 28 of a control device 26.

[0070] The control device 26 is provided by a microcomputer includingthe CPU 28, a random access memory (RAM) 30, a read only memory (ROM)32, an output interface 34, and a display interface 36. The CPU 28processes the input signals SK, SM supplied from the A/D converter 24,by utilizing a temporary-storage function of the RAM 30, according tocontrol programs pre-stored in the ROM 32. The CPU 28 controls the airpump 14 and the pressure regulator valve 16 via the output interface 34,and controls a display 38 via the display interface 36. The display 38includes an image display panel (not shown) which displays an image,such as BP values and waveforms, consisting of a number of pictureelements, and a printer (not shown) which records, on a recording sheetof paper, using an ink, the image currently displayed on the imagedisplay panel. In the present embodiment, the air pump 14, the pressureregulator valve 16, and the control device 26 cooperate with one anotherto provide a cuff-pressure regulating device 52 (FIG. 2) which will bedescribed later.

[0071] A mode switch 40 is manually operable by a user for selectivelyestablishing a BP measure mode and a BP monitor mode. The mode switch 40supplies a mode signal indicative of the selected mode, to the CPU 28. AStart/Stop switch 42 is manually operable by the user for inputting astart command or a stop command to start or stop an operation of thepresent BP monitor, and supplies a command signal indicative of theinput command, to the CPU 28.

[0072]FIG. 2 illustratively shows the various functions of the presentBP monitor. When the mode switch 40 is operated to select the BP measuremode, the cuff-pressure regulating device 52 is operated to increase thepressure of the cuff 10 (hereinafter, referred to as the “cuff pressureP_(c)”) up to a target pressure higher than a systolic BP value of thesubject. While the cuff pressure is increased, or subsequently decreasedfrom the target pressure at a low rate of 2 to 3 mmHg/sec, a BPmeasuring device 50 carries out an oscillometric BP measuring method inwhich a BP value of the subject is measured based on the variation ofrespective amplitudes, A_(n) (n are natural numbers), of a series ofpulses of a pulse wave which is detected from the cuff 10. The BPmeasuring device 50 is provided by the pressure sensor 12, the low-passfilter 20, and the control device 26. The BP measuring device 50performs a BP measurement in the case where the operation of the BPmonitor is started in the BP measure mode. The BP measuring device 50also performs a BP measurement when abnormality identifying means 60(described later) identifies an abnormal change of monitor diastolic BPvalues determined by diastolic-BP determining means 58 (describedlater). The control device 26 functions as both the diastolic-BPdetermining means 58 and the abnormality identifying means 60.

[0073] In the BP monitor mode, the cuff-pressure regulating device 52operates, at a predetermined interval of time, for increasing the cuffpressure P_(c) at a predetermined rate of change. Pulse-amplitudedetermining means 54 determines, by calculation, respective amplitudes,A_(m) (m are natural numbers), of pulses of a pulse wave which isproduced in the cuff 10 in synchronism with the heartbeat of the subjectwhile the cuff pressure is increased by the cuff-pressure regulatingdevice 52. Candidate determining means 56 judges whether an amplitudeA_(m) (m≦i−1) of each of prior pulses determined by the pulse-amplitudedetermining means 54 is not greater than a reference value, A_(a)(=A_(m)×(1−R), where m=i and 0<R<1), which is smaller than an amplitudeA_(m) (m=i) of a subsequent pulse determined by the pulse-amplitudedetermining means 54, by a predetermined proportion, R, of the amplitudeA_(m) of the subsequent pulse. The amplitude of each of the prior pulsesis determined before the amplitude of the subsequent pulse isdetermined. If a positive judgment is made, the candidate determiningmeans 56 determines, as a diastolic BP candidate, P_(ck), of thesubject, a cuff pressure P_(c) detected when each prior pulse isdetected in the cuff 10. The control device 26 functions as both thepulse-amplitude determining means 54 and the candidate determining means56. The diastolic-BP determining means 58 determines, as a monitordiastolic BP value, MBP_(DIA), of the subject, the cuff pressure P_(c)corresponding to the amplitude of a prior pulse, if the candidatedetermining means 56 determines, as a diastolic BP candidate, the cuffpressure P_(c) corresponding to the amplitude of that prior pulse, withrespect to each of a predetermined number, N₀, of the subsequent pulses.

[0074] The abnormality identifying means 60 identifies an abnormality ofthe monitor diastolic BP values MBP_(DIA) determined by the diastolic-BPdetermining means 58, such as an abrupt decrease of the blood pressureof the subject. If the identifying means 60 identifies an abnormality,the BP measuring device 50 is immediately operated for carrying out anoscillometric BP measurement.

[0075] Next, there will be described the operation of the present BPmonitor by reference to the flow charts of FIGS. 3 and 4.

[0076] First, at Step S1, the CPU 28 judges, based on the command signalsupplied from the Start/Stop switch 42, whether the Start/Stop switch 43has been operated to input a start command to start the operation of theBP monitor. If a negative judgment is made at Step S1, the control ofthe CPU 28 repeats Step S1 while waiting for a positive judgment to bemade at Step S1. Meanwhile, if a positive judgment is made, the controlof the CPU 28 proceeds with Step S2 to judge whether the mode switch 40has been operated to select the BP monitor mode. In the case where theBP measure mode is in use, a negative judgment is made at Step S2, sothat the control of the CPU 28 goes to Step S3, i.e., BP measure routineaccording to which a known oscillometric BP measurement is carried outto measure a systolic, a diastolic, and a mean BP value, BP_(SYS),BP_(DIA), BP_(MEAN), of the subject. When the BP measurement isfinished, the pressure regulator valve 16 is opened to quickly deflatethe cuff 10, thereby releasing the upper arm of the subject from thecuff pressure P_(c), i.e., pressing force of the cuff 10. Step S3 isfollowed by Step S4 to store the measured BP values in the RAM 30 andoperate the display 38 to indicate numerals representing the measured BPvalues.

[0077] More specifically described, in the oscillometric BP measurementeffected at Step S3, the air pump 14 and the pressure regulator valve 16are operated to quickly increase the cuff pressure P_(c) up to apredetermined target pressure, P_(cm), e.g., 180 mmHg. Subsequently, theair pump 14 is stopped and the degree of opening of the regulator valve16 is regulated, so that a slow deflation of the cuff 10 is started.That is, the cuff pressure P_(c) is decreased at a low rate of 2 to 3mmHg/sec which is suitable for BP measurements. During this slowcuff-pressure decrease, the control device 26 determines BP valuesaccording to a well known oscillometric BP determining algorithm. Thatis, the CPU 28 determines, as a systolic BP value BP_(SYS), a cuffpressure at the time when the pulse amplitudes A_(n) significantlychange in a phase in which the amplitudes A_(n) increase; determines, asa mean BP value BP_(MEAN), a cuff pressure at the time when theamplitudes A_(n) take a maximum value, i.e., when a pulse having amaximum amplitude is produced; and determines, as a diastolic BP valueBP_(DIA), a cuff pressure at the time when the pulse amplitudes A_(n)significantly change in a phase in which the amplitudes A_(n) decrease.

[0078] In the case where the mode switch 40 has been operated to selectthe BP monitor mode, a positive judgment is made at Step S2 andaccordingly the control of the CPU 28 goes to Step S5 to judge whether atimer has counted up a predetermined monitor cycle time from the timewhen a monitor diastolic BP value MBP_(DIA) had been determined at StepS6 in the preceding control cycle in accordance with the main routine ofFIG. 3. The monitor cycle time may fall in the range of from severalminutes to ten and several minutes. If a negative judgment is made atStep S5, the CPU 28 repeats Step S5 until a positive judgment is made.Meanwhile, if a positive judgment is made at Step S5, the control of theCPU 28 goes to Step S6, i.e., BP monitor routine of FIG. 4.

[0079] At Step S6-1 of FIG. 4, the CPU 28 judges whether the CPU 28 hasreceived, from the band-pass filter 22, a pulse-wave signal SMrepresenting one pulse of a pulse wave. If a negative judgment is madeat Step S6-1, the current control cycle in accordance with the routineof FIG. 4 is ended. On the other hand, if a positive judgment is made atStep S6-1, the control of the CPU 28 goes to Step S6-2 to increase thecuff pressure P_(c) by a predetermined pressure increase amount, ΔP_(c),and subsequently to Step S6-3 to determine, by calculation, an amplitudeA_(m) of the pulse received at Step S6-1 and store, in an appropriatearea of the RAM 30, the determined amplitude A_(m) together with thecuff pressure P_(c) at the time when the pulse is detected through theband-pass filter 22. The cuff pressure P_(c) is read from thecuff-pressure signal SK supplied from the low-pass filter 20. WhileSteps S6-2 and S6-3 are repeated, the cuff pressure P_(c) is increasedat a predetermined rate of change, more specifically, stepwise by therespective pressure amounts ΔP_(c), as shown in FIG. 5. While the cuffpressure P_(c) is held for a short duration at each of the pressuresteps, the CPU 28 reads in one pulse, determines the amplitude A_(m) ofthe pulse, and stores the pulse amplitude A_(m) in the RAM 30. Step S6-3corresponds to the pulse-amplitude determining means 54.

[0080] At Step S6-4, the CPU 28 judges whether the amplitude A_(m)(m≦i−1) of each of the prior pulses determined at Step S6-3 in the priorcontrol cycles before the current control cycle is not greater than areference value A_(a) (e.g., 0.7×A_(m)) which is smaller than theamplitude A_(m) (m=i) of the current pulse determined at Step S6-3 inthe current control cycle, by a predetermined proportion R (e.g., 30%(R=0.3)) of the amplitude A_(m) of the current pulse. If a positivejudgment is made, the CPU 28 determines, as a diastolic BP candidateP_(ck) of the subject, the cuff pressure P_(c) corresponding to thepulse amplitude A_(m) of each prior pulse. While the cuff pressure P_(c)is increased up to a mean BP value BP_(MEAN) of the subject, the pulseamplitudes A_(m) continue to increase as indicated at broken line inFIG. 5A. For example, in the case where the pulse amplitude A₂ isdetermined at Step S6-3, the only prior amplitude A₁ is compared with0.7×(the amplitude A₂). If the amplitude A₁ is greater than 0.7×(theamplitude A₂), the cuff pressure P_(cl) corresponding to the amplitudeA₁ is not determined as a diastolic BP candidate P_(ck). In the exampleshown in FIG. 5B, a negative judgment is made at Step S6-4 for each ofthe amplitudes A₁ to A₄. Once a negative judgment is made for a pulseamplitude A_(m) at Step S6-4, the CPU 28 never makes a judgment for thatamplitude at Step S6-4 in the following control cycles.

[0081] On the other hand, if the CPU 28 makes a positive judgment atStep S6-4, the control of the CPU 28 goes to Step S6-5 to determine thecuff pressure P_(c) corresponding to the pulse amplitude A_(m), as adiastolic BP candidate P_(ck), and store the pressure P_(c) in anappropriate area of the RAM 30. For example, in the case where the pulseamplitude A₆ is determined at Step S6-3, the prior amplitude A₅ iscompared with 0.7×(the amplitude A₆) and, if the amplitude A₅ is notgreater than 0.7×(the amplitude A₆), the cuff pressure P_(c5)corresponding to the amplitude A₅ is determined as a diastolic BPcandidate P_(ck). Thus, a positive judgment is made at Step S6-4 for theamplitude A₅. Regarding the example shown in FIG. 5B, a positivejudgment is made for the amplitude A₅, when the amplitude A₅ is comparedwith the amplitude A₇ in the next cycle, and with the amplitude A₈ inthe cycle after that next cycle. Steps S6-4 and S6-5 correspond to thecandidate determining means 56.

[0082] Step S6-5 is followed by Step S6-6 to judge, regarding each ofthe prior amplitudes A_(m), whether a number, N, of the positivejudgments made for each prior amplitude A_(m) at Step S6-4 becomes notsmaller than a reference number, N₀, e.g., 3. If a positive judgment ismade for any of the prior amplitudes A_(m), a positive judgment isfinally made at Step S6-5. For example, in the example shown in FIG. 5B,when the amplitude A₈ is determined at Step S6-3, a positive judgment ismade for the amplitude A₅ and a negative judgment is made for each ofthe amplitudes A₆ and A₇. Accordingly, a positive judgment is finallymade at Step S6-6. The reference number N₀ is empirically determined asbeing suitable for obtaining a diastolic BP value. In the case where theabove-indicated pressure increase amount ΔP_(c) is about 5 mmHg, thereference number N₀ is determined at 3.

[0083] If a negative judgment is finally made at Step S6-6, i.e., if anegative judgment is made for all the prior amplitudes A_(m), thecontrol of the CPU 28 goes back to Step S6-1. On the other hand, if apositive judgment is finally made at Step S6-6, the control goes to StepS6-7 to determine, as a monitor diastolic BP value MBP_(DIA), the cuffpressure P_(c) corresponding to the pulse amplitude A_(m) for whichthree positive judgments are made at Step S6-4. The thus determined cuffpressure P_(c) is stored in the RAM 30. Regarding the example shown inFIG. 5B, the cuff pressure P_(c5) is determined as a monitor diastolicBP value MBP_(DIA). In the present embodiment, Steps S6-6 and S6-7correspond to the diastolic-BP determining means 58. Step S6-7 isfollowed by Step S6-8 to display the newly determined monitor diastolicBP value MBP_(DIA) in place of the old value MBP_(DIA) determined inStep S6 in the preceding control cycle in accordance with the mainroutine of FIG. 3.

[0084] After the monitor diastolic BP value MBP_(DIA) is determined atStep S6, the control of the CPU 28 goes to Step S7 to judge whether theStart/Stop switch 42 is operated to stop the BP monitoring operation. Ifa positive judgment is made at Step S7, the control goes back to StepS1. On the other hand, if a negative judgment is made at Step S8, thecontrol goes to Step S8 to judge whether an abnormality has occurred tothe monitor diastolic BP values MEP_(DIA). For example, the CPU 28identifies an abnormality of the diastolic BP values MBP_(DIA), if anamount, or a rate, of change of the current value MBP_(DIA) from amoving average of prior values MBP_(DIA) exceeds a reference value,which indicates that the blood pressure of a living subject has abruptlydecreased. Step S8 corresponds to the abnormality identifying means 60.

[0085] If a negative judgment is made at Step S8, the control goes backto Step S5 and repeats Steps S5 to S8. Meanwhile, if a positive judgmentis made at Step S8, the control of the CPU 28 goes to Step S9 to carryout an oscillometric BP measurement using the cuff 10 like at Step S3.Step S9 is followed by Step S10 to operate the display 38 to display themeasured BP values BP_(SYS), BP_(MEAN), BP_(DIA).

[0086] As is apparent from the foregoing description, the present BPmonitor operates such that in the BP monitor mode the amplitudes A_(m)of pulses of a pulse wave which are produced in the cuff 10 while thecuff pressure P_(c) is increased by the cuff-pressure regulating device52, are determined by the pulse-amplitude determining means 54. Inaddition, the candidate determining means 56 judges whether theamplitude A_(m) (m≦i−1) of each of the prior pulses determined in theprior control cycles before the current control cycle is not greaterthan the reference value A_(a) which is smaller than the amplitude A_(m)(m=i) of the current pulse determined in the current control cycle, bythe predetermined proportion R of the amplitude A_(m) of the currentpulse and, if a positive judgment is made, determines, as a diastolic BPcandidate P_(ck) of the subject, the cuff pressure P_(c) correspondingto the amplitude A_(m) of each prior pulse. The diastolic-BP determiningmeans 58 judges, regarding each of the prior amplitudes A_(m), whetherthe number N of the positive judgments made for each prior amplitudeA_(m) becomes not smaller than the reference number N₀ and, if apositive judgment is made for any of the prior amplitudes A_(m),determines, as a monitor diastolic BP value MBP_(DIA), the cuff pressureP_(c) corresponding to the prior amplitude A_(m) for which thepredetermined number N₀ of positive judgments are made. The present BPmonitor has been developed based on the fact that a diastolic BP valueBP_(DIA) does not correspond to a pulse having an amplitude not smallerthan an amplitude, A_(max)×(1−R), smaller than a maximum amplitude,A_(max), of the last pulse that is detected in the current controlcycle, by the predetermined proportion R of the amplitude A_(max) of thelast pulse. The last or current pulse has a maximum amplitude A_(max) ofall the amplitudes A_(m) of the prior pulses which have been detectedprior to the last or current pulse while the cuff pressure P_(c) isincreased, as indicated in FIG. 5A. In addition, the present BP monitorhas been developed based on the fact that an amplitude of a pulsecorrectly corresponding to a diastolic BP value BP_(DIA) does not changeeven if the cuff pressure P_(c) is increased.

[0087] Therefore, the present BP monitor can determine a monitordiastolic BP value at a pressure level higher than the diastolic BPvalue by only the product of the pressure increase amount ΔP_(c) and thereference number N₀. This monitor diastolic BP value enjoys highaccuracy. In addition, since the pressure level where the BP value isdetermined is considerably low, the living subject does not feeldiscomfort.

[0088] In the present embodiment, the cuff-pressure regulating device 52stepwise increases the cuff pressure P_(c), by alternately increasing itby the increment amount ΔP_(c) and holding it at each increased level.The pulse-amplitude determining means 54 determines, by calculation, theamplitude A_(m) of the pulse which is produced when the cuff pressureP_(c) is held at each increased level. The thus determined pulseamplitude A_(m) enjoys high accuracy because it is free from the adverseinfluence resulting from the increasing of the cuff pressure P_(c).Therefore, the monitor BP values are determined with accuracy based onthe pulse amplitudes A_(m).

[0089] In addition, in the present embodiment, when the abnormalityidentifying means 60 identifies an abnormality of the monitor diastolicBP values MBP_(DIA), the BP monitor automatically carries out anoscillometric BP measurement by increasing the cuff pressure P_(c) up toa high level which is estimated to be higher than a systolic BP value ofa living subject. Thus, the BP monitor provides accurate BP values uponidentification of an abnormality of the subject. Therefore, a doctor ora nurse can take an appropriate medical treatment on the subject.

[0090] Although in the illustrated embodiment the pressure P_(c) of thecuff 10 is stepwise increased at a predetermined rate in the BP monitormode, it is possible that the cuff pressure P_(c) be continuouslyincreased at a predetermined rate.

[0091] While in the illustrated embodiment the pressure increase amountΔP_(c) is a constant value, it is possible that the pressure increaseamount ΔP_(c) be variable depending upon the current cuff pressureP_(c).

[0092] Although in the illustrated embodiment the predeterminedproportion R used at Step S6-4 is a constant value, it is possible thatthe CPU 28 determine a value R based on the variation of the amplitudesof pulses of a pulse wave obtained in the oscillometric BP measurementeffected at Step S3. In the latter case, the BP monitor can determine avalue R suitable for each individual subject.

[0093] While in the illustrated embodiment the reference number N₀ usedat Step S6-6 is a constant value, it is possible that the CPU 28determine a number N₀ based on the variation of the amplitudes of pulsesof a pulse wave obtained in the oscillometric BP measurement effected atStep S3. In the latter case, the BP monitor can determine a number N₀suitable for each individual subject.

[0094] In the illustrated embodiment, the BP measuring device 50performs an oscillometric BP measurement at Step S3 when the operationof the BP monitor is started in a state in which the BP measure mode hasbeen selected, or the abnormality identifying means 60 identifies anabnormality of the monitor diastolic BP values determined by thediastolic-BP determining means 58. However, it is possible to adapt theBP measuring device 50 to periodically perform an oscillometric BPmeasurement at a predetermined cycle time, i.e., at a predeterminedinterval of time.

[0095] Referring next to FIGS. 7 to 12, there will be described acontinuous blood pressure (BP) monitor 100 as a second embodiment of thepresent invention. The BP monitor 100 may be used to monitor BP valuesof a patient who is undergoing, or has undergone, a surgical operation.

[0096] In FIG. 7, the BP monitor 100 includes an inflatable cuff 110including a rubber bag and a band-like cloth bag in which the rubber bagis accommodated. The cuff 110 is wound around, e.g., an upper arm 112 ofa patient. The cuff 110 is connected via piping 120 to a pressure sensor114, a selector valve 116, and a first air pump 118. The selector valve116 is selectively placed, under control of an electronic control device128, in a first state in which the valve 116 permits pressurized air tobe supplied from the air pump 118 to the cuff 110 to increase quicklythe air pressure of the cuff 110 (hereinafter, referred to as the “cuffpressure”), a second state in which the valve 116 causes the cuff 110 tobe deflated slowly, and a third state in which the valve 116 causes thecuff 110 to be deflated quickly.

[0097] The pressure sensor 114 detects the cuff pressure (i.e., airpressure in the cuff 110), and generates a pressure signal, SP,representing the detected cuff pressure. The pressure signal SP issupplied to each of a static-pressure filter circuit 122 and apulse-wave filter circuit 124. The static-pressure filter circuit 122includes a low-pass filter which extracts, from the pressure signal SP,a cuff-pressure signal, SK, representative of a static or direct-currentcomponent of the pressure signal SP. The cuff-pressure signal SK issupplied via a first analog-to-digital (A/D) converter 126 to thecontrol device 128.

[0098] The pulse-wave filter circuit 124 includes a band-pass filterwhich extracts, from the pressure signal SP, a pulse-wave signal, SM₁,representative of an oscillating or alternating-current component of thepressure signal SP. The pulse-wave signal SM₁ is supplied via a secondA/D converter 130 to the control device 128. The alternating-currentcomponent represented by the pulse-wave signal SM₁ corresponds to anoscillatory pressure wave, i.e., pulse wave which is produced from abrachial artery (not shown) of the patient in synchronism with theheartbeat of the patient and is propagated via skin tissue to the cuff110. This pulse wave is referred to as the “cuff pulse wave (CPW)” to bedistinguished from a “pressure pulse wave (PPW)” which will be describedlater. In the present embodiment, the cuff 110, the pressure sensor 114,and the pulse-wave filter circuit 124 cooperate with one another toprovide a cuff pulse wave sensor.

[0099] The control device 128 is provided by a microcomputer including acentral processing unit (CPU) 129, a read only memory (ROM) 131, arandom access memory (RAM) 133, and an input and output (I/O) port (notshown). The CPU 129 processes input signals, including the signals SK,SM₁, by utilizing a temporary-storage function of the RAM 133, accordingto control programs pre-stored in the ROM 131. In addition, the CPU 129supplies drive signals via the I/O port to drive circuits (not shown)associated with the selector valve 116 and the air pump 118,respectively. Thus, the CPU 129 controls respective operations of thevalve 116 and the pump 118. For example, when an oscillometric BPmeasurement using the cuff 110 is carried out to calibrate the presentBP monitor 100, the CPU 129 controls the valve 116 and the pump 118 toincrease quickly the cuff pressure up to a predetermined target valueand subsequently decrease the cuff pressure at a low rate of 2 to 3mmHg/sec. Based on the variation of the cuff pulse wave represented bythe pulse-wave signal SM₁ provided by the pulse-wave filter circuit 124during the low-rate decreasing of the cuff pressure, the CPU 129determines a systolic, a mean, and a diastolic BP value of the patient,according to a known oscillometric BP measuring method. In addition, theCPU 129 controls a display 132 to display the thus determined BP values.

[0100] A pressure-pulse-wave (PPW) detecting probe 134 includes acontainer-like sensor housing 136, and a fastening band 140 connected tothe sensor housing 136. With the help of the fastening band 140, the PPWdetecting probe 134 is detachably attached to a wrist 142 of the samearm 112 of the patient on which the cuff 110 is worn, such that anopening of the sensor housing 136 is opposed to a body surface 138 ofthe patient. A PPW sensor 146 is secured via an elastic diaphragm 144 toinner surfaces of the sensor housing 136 such that the PPW sensor 146 ismovable relative to the housing 136 and is advanceable through theopening of the housing 136 toward the body surface 138 of the patient.The sensor housing 136 and the diaphragm 144 cooperate with each otherto define a pressure chamber 148, which is supplied with pressurized airfrom a second air pump 150 via a pressure regulator valve 152. Thus, thePPW sensor 146 is pressed on the body surface 138 with a pressing force,P_(HD), corresponding to an air pressure in the chamber 148. In thepresent embodiment, the pressing forces of the PPW sensor 146 applied tothe body surface 138 or a radial artery 156 are indicated in terms ofpressure values (mmHg) in the chamber 148. The sensor housing 136, thediaphragm 144, the pressure chamber 148, the second air pump 150, thepressure regulator valve 152, etc. cooperate with one another to providea pressing device which presses the PPW sensor 146 against the radialartery 156 via the body surface or skin tissue 138.

[0101] The PPW sensor 146 includes a semiconductor chip formed of amonocrystalline silicon which has a press surface 154, and a number ofpressure-sensing semiconductor elements (not shown) which are arranged,in the press surface 154, in an array at a regular interval of distance(about 0.2 mm), such that the array of pressure-sensing elements extendsin the direction of width of the radial artery 156. When the PPW sensor146 is pressed against the radial artery 156 via the body surface 138 ofthe wrist 142, the PPW sensor 146 detects an oscillatory pressure wave,i.e., pressure pulse wave (PPW) which is produced from the radial artery156 in synchronism with the heartbeat of the patient and is propagatedvia the body surface 138 to the PPW sensor 146. The PPW sensor 146generates a PPW signal, SM₂, representing the detected PPW, and suppliesthe PPW signal SM₂ to the control device 128 via a third A/D converter158. An example of the PPW (i.e., PPW signal SM₂) detected by the PPWsensor 146 is illustrated in the graph of FIG. 8.

[0102] The CPU 129 of the control device 128 processes the inputsignals, including the PPW signal SM₂, by utilizing thetemporary-storage function of the RAM 133, according to the controlprograms pre-stored in the ROM 131, and supplies drive signals to drivecircuits (not shown) associated with the second air pump 150 and thepressure regulator valve 152, respectively. Thus, the CPU 129 controlsrespective operations of the pump 150 and the valve 152 to regulate theair pressure of the pressure chamber 148 applied to the PPW sensor 146,i.e., the pressing force P_(HD) of the PPW sensor 146 applied to theradial artery 156 via the body surface or skin tissue 138.

[0103] When a continuous BP monitoring operation is carried out, the CPU129 determines an optimum pressing force, P_(HDO), of the PPW sensor 146applied to the radial artery 156, based on the PPW (signal SM₂) detectedby the PPW sensor 146 while the pressure of the pressure chamber 148 isslowly changed, and controls the pressure regulator valve 152 tomaintain the pressure of the chamber 148 at the determined optimumpressing force P_(HDO). In addition, the CPU 129 determines arelationship between BP values and PPW magnitudes P_(M) (i.e., voltagevalues of the signal SM₂), based on a systolic and a diastolic BP value,BP_(SYS), BP_(DIA), measured using the cuff 110 according theoscillometric BP measuring method, and a maximum and a minimummagnitude, P_(Mmax), P_(Mmin), of one heartbeat-synchronous pulse of thePPW detected by the PPW sensor 146 being pressed on the body surface 138with the optimum pressing force P_(HDO). According to the thusdetermined relationship, the CPU 129 determines a systolic and adiastolic BP value (i.e., monitor BP values), MBP_(SYS), MBP_(MEAN),MBP_(DIA), of the patient, based on a maximum magnitude (i.e.,upper-peak magnitude) P_(Mmax), a mean magnitude (described later),P_(Mmean), and a minimum magnitude (i.e., lower-peak magnitude),P_(Mmin), of each of successive heartbeat-synchronous pulses of the PPWdetected by the PPW sensor 146 being pressed with the optimum pressingforce P_(HDO). Subsequently, the CPU 129 controls the display 132 tosuccessively display, for each heartbeat-synchronous pulse, the thusdetermined monitor BP values MBP_(SYS), MBP_(MEAN), MBP_(DIA), indigits, and continuously display the waveform of the PPW detected by thePPW sensor 146. This waveform represents the instantaneous monitor BPvalues MBP of the patient.

[0104]FIG. 9 shows an example of a relationship between BP values MBP(monitor BP values) and PPW magnitudes P_(M) that is determined by thecontrol device 128 or the CPU 129. This relationship is expressed by thefollowing linear function:

MBP=A·P _(M) +B

[0105] where A is a constant corresponding to the slope of the linearfunction and B is a constant corresponding to the intercept of the axisof ordinate indicative of the monitor BP values MBP.

[0106]FIG. 10 illustrates various functions of the electronic controldevice 128 of the continuous BP monitor 100. The pressing pressure ofthe cuff 110 is detected by the pressure sensor 114. The static-pressurefilter circuit 122 cooperates with the control device 128 to provide aBP measuring device 172 which measures, according to an oscillometric BPmeasuring method (JIS T 1115; JIS is Japanese Industrial Standard), asystolic BP value BP_(SYS), a mean BP value BP_(MEAN), and a diastolicBP value BP_(DIA)of a living subject based on the variation ofrespective amplitudes of heartbeat-synchronous pulses of the cuff pulsewave (CPW) detected by the CPW sensor 114, 124, 130 while the pressureof the cuff 110 is slowly increased or decreased at the rate of 2 to 3mmHg/sec. The cuff pulse wave is represented by the pulse-wave signalSM₁ obtained through the pulse-wave filter circuit 124. The PPW sensor146 is worn on the wrist 142 of the same arm 112 of the patient on whichthe cuff 110 is worn, and detects the PPW produced from the radialartery 156 downstream of the brachial artery being pressed by the cuff110. The control device 128 functions as a relationship determiningmeans 174 which determines a MBP-P_(M) relationship between monitor BPvalues MBP and PPW magnitudes P_(M) that is expressed by the linearfunction shown in FIG. 9, based on the PPW detected by the PPW sensor146 and the BP values measured by the BP measuring device 172. Thecontrol device 128 also functions as a monitor-BP (MBP) determiningmeans 176 which successively determines, according to the MBP-P_(M)relationship, a monitor BP value MBP of the subject based on a magnitudeof each of heartbeat-synchronous pulses of the PPW detected by the PPWsensor 146. The selector valve 116 and the first air pump 118 cooperatewith the control device 128 to provide a cuff-pressure regulating device178 which regulates the air pressure of the cuff 110 (i.e., cuffpressure) that is detected by the pressure sensor 114. The cuff-pressureregulating device 178 changes the cuff pressure according to awell-known procedure, so that the BP measuring device 172 can measure BPvalues of the patient using the cuff 10 and the relationship determiningmeans 174 calibrates the MBP-P_(M) relationship based on the BP valuesmeasured using the cuff 110. For example, the regulating device 178increases the cuff pressure up to a target value, e.g., 180 mmHg, whichis higher than an estimated systolic BP value of the patient andsubsequently decreases the cuff pressure slowly at the rate of 2 to 3mmHg/sec, during a measurement period in which BP values of the patientare determined by the BP measuring device 172 according to a well-knownoscillometric BP determining algorithm. After the BP measuringoperation, the regulating device 178 quickly deflates the cuff 110. Inaddition, the cuff-pressure regulating device 178 provides acuff-pressure increasing means 178 which continuously or stepwiseincreases the cuff pressure at a predetermined rate.

[0107] Moreover, the control device 128 functions as awaveform-characteristic determining means 180 which determines acharacteristic of a lower-peak portion of a waveform of each ofsuccessive heartbeat-synchronous pulses of the pressure pulse wave (PPW)which are detected by the PPW sensor 146 when the cuff pressure isincreased at the predetermined rate by the cuff-pressure increasingmeans 178. The lower-peak portion of the waveform of each pulse includesa lower-peak point of each pulse. In addition, the control device 128functions as a judging means 182 which judges whether the relationshipdetermined by the relationship determining means 174 is accurate, basedon at least one diastolic BP value BP_(DIA) determined by the bloodpressure determining means 176 and a cuff pressure corresponding to atime when the waveform characteristics detected by thewaveform-characteristic determining means 180 significantly largelychange.

[0108] Next, there will be described the operation of the BP monitor 100constructed as described above, by reference to the flow chart of FIG.11 representing a control program pre-stored in the ROM 131.

[0109] First, at Step S101, the CPU 129 of the control device 128controls the second air pump 150 and the pressure regulator valve 152 toincrease slowly the pressure of the pressure chamber 148, anddetermines, as an optimum pressing force P_(HDO), a pressure P_(HD) ofthe chamber 148 when the PPW sensor 146 detects a maximum pulse havingthe greatest amplitude of respective amplitudes of all the pulsesdetected thereby during the slow increasing of the pressure of thechamber 148. Subsequently, the CPU 129 maintains or holds the pressureof the chamber 148 at the thus determined optimum pressing forceP_(HDO). Thus, the optimum pressing force P_(HDO) is applied to the PPWsensor 146 to press the radial artery 156 via the body surface 138.

[0110] Next, the control of the CPU 129 proceeds with Step S102 to judgewhether a relationship as shown in FIG. 9 has been determined for aparticular patient on which the cuff 110 is worn. If a positive judgmentis made at Step S102, the control of the CPU 129 goes to Step S103.Since, however, initially a negative judgment is made at Step S102, thecontrol goes to Step S107 corresponding to the BP measuring device 172.Specifically described, the selector valve 116 is switched to the firststate and the first air pump 118 is operated, so that the cuff pressureis increased up to a target pressure (e.g., 180 mmHg) higher than anestimated systolic BP value of the patient. Subsequently, the air pump118 is stopped and the selector valve 116 is switched to the secondstate, so that the cuff pressure is decreased at a predetermined lowrate (e.g., about 3 mmHg/sec). Based on the variation of respectiveamplitudes of heartbeat-synchronous pulses of the cuff-pulse-wave (CPW)signal SM₁ obtained during this slow decreasing of the cuff pressure,the CPU 129 determines a systolic, a mean, and a diastolic BP valueBP_(SYS), BP_(MEAN), BP_(DIA) of the patient according to a knownoscillometric BP determining algorithm. More specifically, the CPU 129determines, as the systolic BP value BP_(SYS), a cuff pressure at thetime when the pulse amplitudes significantly largely increase,determines, as the diastolic BP value BP_(DIA), a cuff pressure at thetime when the pulse amplitudes, significantly largely decrease, anddetermines, as the mean BP value BP_(MEAN), a cuff pressure at the timewhen the pulse amplitudes become maximum. In addition, the CPU 129determines a pulse rate of the patient based on the time intervalbetween respective upper-peak points of two successiveheartbeat-synchronous pulses of the CPW signal SM₁. The thus measured BPvalues and pulse rate are stored in the RAM 133 and displayed by thedisplay 132. Then, the selector valve 116 is switched to the thirdstate, so that the cuff pressure is quickly decreased or deflated.

[0111] Subsequently, the control of the CPU 129 goes to Step S108 todetermine a relationship between monitor BP value MBP and magnitudeP_(M) of pressure pulse wave (i.e., voltage of the pressure-pulse-wave(PPW) signal SM₂) as shown in FIG. 9. More specifically, the CPU 129newly reads in one heartbeat-synchronous pulse of the PPW signal SM₂supplied from the PPW sensor 146, determines a maximum and a minimummagnitude P_(Mmax), P_(Mmin) of the one pulse, and determines thepreviously-indicated linear function based on the systolic and diastolicBP values BP_(SYS), BP_(DIA) of the patient measured at Step S107 andthe thus determined maximum and minimum magnitudes P_(Mmax), P_(Mmin) ofthe one pulse of the PPW signal SM₂. Step S108 corresponds to therelationship determining means 174.

[0112] After the MBP-P_(M) relationship shown in FIG. 9 is determined atStep S108, the control of the CPU 129 goes to Step S109 and thefollowing steps to carry out a continuous BP monitoring operation.First, at Step S109, the CPU 129 judges whether the CPU 129 has read inone heartbeat-synchronous pulse of the PPW signal SM₂ supplied from thePPW sensor 146 being pressed at the optimum pressing force P_(HDO). If anegative judgment is made at Step S109, the CPU 129 waits for detectingone pulse of the PPW signal SM₂. Meanwhile, if a positive judgment ismade at Step S109, the control of the CPU 129 goes to Step S110 todetermine a maximum (upper-peak) magnitude P_(Mmax) and a minimum(lower-peak) magnitude P_(Mmin) of the one pulse of the PPW signal SM₂.In addition, the CPU 129 determines a mean magnitude, P_(Mmean), of theone pulse in a known manner. For example, the CPU 129 determines, as themean magnitude P_(Mmean) of one pulse, a signal-related one of thevarycentric coordinates of an area defined by the waveform of the onepulse and a base line passing through the lower-peak point of the onepulse, the base line being indicated at two-dot chain line in FIG. 8.The pulse area is calculated by first subtracting the magnitude of thelower-peak point from the magnitude of each sampling point on thewaveform of the one pulse of the signal SM₂ and then summing up the thusobtained values. Step S110 is followed by Step S111 to determine asystolic, a mean, and a diastolic BP value MBP_(SYS), MBP_(MEAN),MBP_(DIA) (monitor BP values) of the patient, based on the maximum,mean, and minimum magnitudes P_(Mmax), P_(Mmean), P_(Mmin) of the onepulse of the PPW signal SM₂ determined at Step S110, according to theMBP-P_(M) relationship determined at Step S108. The CPU 129 controls thedisplay 132 to display, on its image display panel, not only the thusdetermined monitor BP values MBP but also the waveform of the one pulsethat is continuous with the respective waveforms of the prior pulses.Steps S110 and S111 correspond to the monitor-BP determining means 176.

[0113] Subsequently, the control of the CPU 129 goes to Step S112 tojudge, based on a timer, whether a predetermined period of 10 to 20minutes has passed after the current MBP-P_(M) relationship isdetermined at Step S108. If a negative judgment is made at Step S112,the control goes back to Step S109 and the following steps to continuethe continuous BP monitoring routine. Thus, the present BP monitor 100successively determines, for each heartbeat-synchronous pulse of thesignal SM₂, a systolic, a mean, and a diastolic BP value MBP_(SYS),MBP_(MEAN), MBP_(DIA) of the patient and displays the determined BPvalues on the display 132. On the other hand, if a positive judgment ismade at Step S112, the CPU 129 resets the timer to zero, and the controlof the CPU 129 goes back to Step S102.

[0114] In the current control cycle, a positive judgment is made at StepS102 because a MBP-P_(M) relationship has been determined at Step S108in the preceding control cycle. Then, the control of the CPU 129 goes toStep S103 to continuously or stepwise increase the cuff pressure fromatmospheric pressure at a predetermined rate of 5 to 20 mmHg/sec anddetermine a characteristic of a lower-peak portion, F (FIG. 8), of thewaveform of each of successive heartbeat-synchronous pulses of thesignal SM₂ which is detected by the PPW sensor 146 when the cuffpressure is increased at the predetermined rate. This characteristic maybe a length, L, of the lower-peak portion F defined by the magnitudeP_(Mmin) of the lower-peak point and a magnitude, P₁, greater by apredetermined amount than the magnitude P_(Mmin), as illustrated in FIG.8. Step S103 corresponds to the cuff-pressure increasing means 178 andthe waveform-characteristic determining means 180. Step S103 is followedby Step S104 to judge whether the CPU 129 has identified a point or atime when the characteristic values L have significantly largelychanged. For example, the CPU 129 differentiates the characteristicvalues L by subtracting, from each value L_(i), the preceding valueL_(i−1) and determines, as an inflection point, K₁, a pointcorresponding to the greatest differential, as illustrated in FIG. 12.

[0115] When the cuff pressure takes values between the systolic anddiastolic BP values of the patient, the lower-peak portion of thewaveform of each pulse of the signal SM₂ is cut off, because thetransmission of the PPW (i.e., blood flow) from the upstream side of thecuff 110 to the downstream side of the same is partially interrupted bythe cuff 110. As the cuff pressure increases, the respective lengths ofthe cut-off portions of the pulses increase and accordingly therespective lengths L of the lower-peak portions of the pulses increase.Therefore, the above-indicated point K₁ is indicative of a time when thecuff pressure is equal to an actual or true diastolic BP value of thepatient. Initially, a negative judgment is made at Step, S104, and thecontrol of the CPU 129 goes back to Step S103. If a positive judgment ismade at Step S104 while Steps S103 and S104 are repeated, the controlgoes to Step S105 to determine a cuff pressure, P_(CD1), correspondingto the point K₁ identified at Step S104 and store it in the RAM 133. Thecuff pressure P_(CD1) is indicative of a true diastolic BP value of thepatient. Step S105 functions as a diastolic BP determining means.

[0116] Step S105 is followed by Step S106 to judge whether the currentMBP-P_(M) relationship determined at Step S108 is accurate, based on thelast diastolic BP value MBP_(DIA) determined at Step S111 and the cuffpressure P_(CD1) (i.e., true diastolic BP value) stored at Step S105.For example, the CPU 129 judges whether the absolute value of thedifference of the last diastolic BP value MBP_(DIA) and the cuffpressure P_(CD1), i.e., |MBP_(DIA)−P_(CD1)|, is not greater than areference value, ΔP₁. This reference value is employed for guaranteeingthe accuracy of the MBP-P_(M) relationship: The reference value is,e.g., 5 mmHg. However, in the case where there is a difference betweenthe cuff pressure P_(CD1) and the diastolic BP value BP_(DIA) measuredat Step S107, the first difference |MBP_(DIA)−P_(CD1)| is compared witha modified reference value obtained in advance by subtracting, from thereference value ΔP1, the second difference between the cuff pressureP_(CD1) and the diastolic BP value BP_(DIA) measured using the cuff 110.Step S106 corresponds to the relationship-accuracy judging means 186.

[0117] If a positive judgment is made at Step S106, the currentMBP-P_(M) relationship is accurate and appropriate, therefore need notbe updated. Therefore, the control of the CPU 129 skips Steps S107 andS108 and goes to Step S109 and the following steps, i.e., the continuousBP monitoring routine. On the other hand, if a negative judgment is madeat Step S106, the control goes to Steps S107 and S108 to carry out anoscillometric BP measurement and determine a new MBP-P_(M) relationshipand subsequently goes to the continuous BP monitoring routine.

[0118] As is apparent from the foregoing description relating to thesecond embodiment shown in FIGS. 7 to 12, the CPU 129 of the controldevice 128 determines, at Step S103, a length L of a lower-peak portionF of the waveform of each of successive heartbeat-synchronous pulses ofthe PPW signal SM₂ which is detected while the cuff pressure isincreased at a predetermined rate. At Step S105, the CPU 129 determinesa cuff pressure P_(CD1) corresponding to a point K₁ or time when thedetermined lengths L significantly largely change. At Step S106, the CPU129 judges whether the current MBP-P_(M) relationship determined at StepS108 is accurate, based on the determined cuff pressure P_(CD1) and thelast diastolic BP value MBP_(DIA) last determined at Step S111. If apositive judgment is made at Step S106, an oscillometric BP measuringoperation is not carried out at Step S107 and the current relationshipis not updated at Step S108, i.e., is maintained. Thus, the patient isprevented from being pressed by the cuff 110. In addition, although thePPW sensor 146 is worn at a position downstream of the cuff 110, thecontinuous BP monitoring operation is continued at Steps S109-S111,without being interrupted due to the inflation of the cuff 110.

[0119] In the second embodiment, since the judgment about whether thecurrent MBP-P_(M) relationship is accurate is made based on the cuffpressure P_(CD1) and the last monitor diastolic BP value MBP_(DIA)determined at Step S111, it is more accurate than a judgment made basedon a monitor diastolic BP value MBP_(DIA) determined at Step S111 apredetermined time before, or the last diastolic BP value BP_(DIA)measured at Step S107.

[0120] Referring next to FIGS. 13 through 16, there will be described athird embodiment of the present invention. The third embodiment relatesto a continuous BP monitor 200 having the same hardware construction asthat of the second embodiment shown in FIG. 7. The same referencenumerals as used in the second embodiment are used to designate thecorresponding elements or parts of the third embodiment and thedescription thereof is omitted.

[0121] However, as shown in FIG. 13, the BP monitor 200 has differentfunctions from those of the BP monitor 100 as the second embodiment. Acontrol device 128 of the BP monitor 200 functions as a phase-differencedetermining means 298 which determines a phase difference, T (msec), ofrespective lower-peak points of each of successive heartbeat-synchronouspulses of a PPW signal SM₂ and a corresponding one of successiveheartbeat-synchronous pulses of a CPW SM₁, as illustrated in the graphof FIG. 15. Those pulses of the signal SM₂ and those pulses of thesignal SM₁ are detected by a PPW sensor 146 and a CPW sensor 114, 124,130, respectively, when a pressure of a cuff 110 is increased at apredetermined rate by a cuff-pressure increasing means 178. The controldevice 128 also functions as a judging means 286 which judges whether anMBP-P_(M) relationship determined by a relationship determining means174 is accurate, based on one or more diastolic blood pressure valuesdetermined by a monitor-BP determining means 176 and a cuff pressurecorresponding to a point, K₂, (FIG. 16) or a time when the phasedifferences T determined by the phase-difference determining means 298significantly largely change.

[0122]FIG. 14 shows a flow chart representing a control programaccording to which the control device 128 controls the operation of thepresent BP monitor 200. The flow chart of FIG. 14 is different from thatof FIG. 11 only in that Step S104 of FIG. 11 is replaced by Step S214 ofFIG. 14 that corresponds to the phase-difference determining means 298.At Step S103, a CPU 129 controls the cuff-pressure increasing means 178to start increasing the cuff pressure.

[0123] At Step S214, first, the PPW sensor 146 and the CPW sensor 114,124, 130 obtain the PPW signal SM₂ and the CPW signal SM₁, respectively,and the CPU 129 determines a phase difference T of respective lower-peakpoints of each of successive heartbeat-synchronous pulses of the PPWsignal SM₂ and a corresponding one of successive heartbeat-synchronouspulses of the CPW SM₁, as shown in FIG. 15. Then, the CPU 129 judgeswhether the CPU 129 has identified a point or a time when the phasedifferences T have significantly largely changed. For example, the CPU129 differentiates the phase-difference values T by subtracting, fromeach value T_(i), the preceding value T_(i−1) and determines, as aninflection point, K₂, a point corresponding to the greatestdifferential, as illustrated in FIG. 16. When the cuff pressure takesvalues between the systolic and diastolic BP values of the patient, thelower-peak portion of the waveform of each pulse of the PPW signal SM₂is cut off, as described above. The point K₂ is indicative of a timewhen the cuff pressure is equal to an actual or true diastolic BP valueof the patient. If a positive judgment is made at Step S214, the controlgoes to Step S105 to determine a cuff pressure PCDI corresponding to thepoint K₂ identified at Step S214 and store it in a RAM 133. Thus, thecuff pressure P_(CD1) is indicative of an actual diastolic BP value ofthe patient. Step S105 is followed by Step S106 to judge whether thecurrent MBP-P_(M) relationship determined at Step S108 is accurate,based on the last diastolic BP value MBP_(DIA) determined at Step S111and the cuff pressure P_(CD1) stored at Step S105. For example, the CPU129 judges whether the absolute value of the difference of the lastdiastolic BP value MBP_(DIA) and the cuff pressure P_(CD1), i.e.,|MBP_(DIA)−P_(CD1)|, is not greater than a reference value, ΔP₁. Thisreference value is, e.g., 5 mmHg.

[0124] As is apparent from the foregoing description relating to thethird embodiment shown in FIGS. 13 to 16, the CPU 129 of the controldevice 128 determines, at Step S214, a phase difference T of respectivelower-peak points of each of the pulses of the PPW signal SM₂ and acorresponding one of the pulses of the PPW signal SM₁ which are obtainedby the PPW sensor 146 and the CPW sensor 114, 124, 130 while the cuffpressure is increased at a predetermined rate at Step S103. At StepS105, the CPU 129 determines a cuff pressure P_(CD1) corresponding to apoint K₂ or time when the determined phase differences T significantlylargely change. At Step S106, the CPU 129 judges whether the currentMBP-P_(M) relationship determined at Step S108 is accurate, based on thedetermined cuff pressure P_(CD1) and the-last diastolic BP valueMBP_(DIA) last determined at Step S111. If a positive judgment is madeat Step S106, an oscillometric BP measuring operation is not carried outat Step S107 and the current relationship is maintained without beingupdated at Step S108. Thus, the patient is prevented from being pressedby the cuff 110. In addition, although the PPW sensor 146 is worn at aposition downstream of the cuff 110, a continuous BP monitoringoperation may be continued at Steps S109-S111 without being interrupteddue to the inflation of the cuff 110.

[0125] Referring to FIGS. 17 and 18, there will be described a fourthembodiment of the present invention. The fourth embodiment relates to acontinuous BP monitor 300 having the same hardware construction as thatof the second embodiment shown in FIG. 7. The same reference numerals asused in the second embodiment are used to designate the correspondingelements or parts of the fourth embodiment and the description thereofis omitted.

[0126] However, as shown in FIG. 17, the BP monitor 300 has differentfunctions from those of the BP monitor 100 as the second embodiment. Acontrol device 128 of the BP monitor 300 functions as a pulse-areacalculating means 388 which calculates an area, S_(M), defined by eachof successive heartbeat-synchronous pulses of a PPW signal SM₂ which isobtained by a PPW sensor 146 when a pressure of an inflatable cuff 110is increased at a predetermined rate by a cuff-pressure increasing means178. The control device 128 also functions as a half-area identifyingmeans 390 which identifies that the pulse areas S_(M) calculated by thepulse-area calculating means 388 have decreased to half an initial pulsearea, S₀, measured before the cuff-pressure increasing means 178 startsincreasing the cuff pressure; and a judging means 392 which judgeswhether a MBP-P_(M) relationship determined by a relationshipdetermining means 174 is accurate, based on one or more mean BP valuesMBP_(MEAN) determined by a monitor-BP determining means 176 and a cuffpressure corresponding to a time when the pulse areas S_(M) havedecreased to half the initial pulse area S₀.

[0127]FIG. 18 shows a flow chart representing a control programaccording to which the control device 128 controls the operation of thepresent BP monitor 300. The flow chart of FIG. 18 is different from thatof FIG. 11 in that in FIG. 18, Step S324 is inserted between Steps S102and S103 of FIG. 11 and Steps S325, S326, S327, and S328 replace StepsS104, S105, and S106 of FIG. 11.

[0128] At Step S324, a CPU 129 of the control device 128 calculates anarea S₀ defined by one heartbeat-synchronous pulse of the signal SM₂produced by the PPW sensor 146 before the cuff pressure is increased atStep S103. For example, the pulse area S₀ is defined by the waveform ofone pulse and a base line, indicated at two-dot chain line in FIG. 2,which passes through the lower-peak point of the one pulse. The-pulsearea S₀ is calculated by first subtracting the magnitude of thelower-peak point from the magnitude of each sampling point on thewaveform of the one pulse of the signal SM₂ and then summing up the thusobtained values.

[0129] After the increasing of the cuff pressure at a predetermined rateis started at Step S103, the CPU 129 calculates, at Step S325, an areaS_(M) of each of heartbeat-synchronous pulses of the PPW signal SM₂obtained while the cuff pressure is increased, in the same manner asthat employed at Step S324. Step S325 corresponds to the pulse-areacalculating means 388.

[0130] Step S325 is followed by Step S326 to calculate a ratio,S_(M)/S₀, of each pulse area S_(M) to the initial pulse area S₀ andjudge whether the ratio S_(M)/S₀ has decreased down to smaller than areference value, K, which is selected at, e.g., ½ providing a basis forjudging whether the cuff pressure has increased up to a value equal to amean BP value of the patient. Step S326 corresponds to the half-areaidentifying means 390.

[0131] If a negative judgment is made at Step S326, Steps S103, S325 andS326 are repeated. Meanwhile, if a positive judgment is made at StepS326, the control of the CPU 129 goes to Step S327 to determine a cuffpressure, P_(CM), at the time when the pulse areas S_(M) have decreasedto half the initial pulse area S₀. This cuff pressure P_(CM) is equal toan actual mean BP value of the patient. The cuff pressure P_(CM) isstored in a RAM 133. Step S327 functions as a mean BP value determiningmeans.

[0132] Step S327 is followed by Step S328 to judge whether the currentMBP-P_(M) relationship determined at Step S108 is accurate, based on thelast mean BP value MBP_(MEAN) determined at Step S111 and the cuffpressure P_(CM) (i.e., actual mean BP value) stored at Step S327. Forexample, the CPU 129 judges whether the absolute value of the differenceof the last mean BP value MBP_(MEAN) and the cuff pressure P_(CM), i.e.,|MBP_(MEAN)−P_(CM)|, is not greater than a reference value, ΔP₂. Thisreference value is employed for guaranteeing the accuracy of theMBP-P_(M) relationship. The reference value is, e.g., 5 mmHg. However,in the case where there is a difference between the cuff pressure P_(CM)and the mean BP value BP_(MEAN) measured at Step S107, the firstdifference |MBP_(MEAN)−P_(CM)| is compared with a modified referencevalue obtained in advance by subtracting, from the reference value ΔP₂,the second difference between the cuff pressure P_(CM) and the mean BPvalue BP_(MEAN) measured using the cuff 110. Step S328 corresponds tothe relationship-accuracy judging means 392.

[0133] If a positive judgment is made at Step S328, the currentMBP-P_(M) relationship is accurate and appropriate, therefore need notbe updated. Therefore, the control of the CPU 129 skips Steps S107 andS108 and goes to Step S109 and the following steps to continue thecontinuous BP monitoring routine. On the other hand, if a negativejudgment is made at Step S328, the control goes to Steps S107 and S108to carry out an oscillometric BP measurement and determine a newMBP-P_(M) relationship and subsequently resumes the continuous BPmonitoring routine.

[0134] As is apparent from the foregoing description relating to thefourth embodiment shown in FIGS. 17 and 18, the CPU 129 of the controldevice 128 determines, at Step S325, an area S_(M) of each ofheartbeat-synchronous pulses of the PPW signal SM₂ obtained by the PPWsensor 146 while the cuff pressure is increased at a predetermined rateat Step S103. At Step S326, the CPU 129 judges whether the pulse areasS_(M) have decreased to half the initial pulse area S₀ and determines,at Step S327, a cuff pressure P_(CM) corresponding to a time when thepulse areas S_(M) have become half. At Step S328, the CPU 129 judgeswhether the current MBP-P_(M) relationship determined at Step S108 isaccurate, based on the determined cuff pressure P_(CM) and the last meanBP value MBP_(MEAN) last determined at Step S111. If a positive judgmentis made at Step S328, an oscillometric BP measuring operation is notcarried out at Step S107 and the current relationship is maintainedwithout being updated at Step S108. Thus, the patient is prevented frombeing pressed by the cuff 110. In addition, although the PPW sensor 146is worn at a position downstream of the cuff 110, a continuous BPmonitoring operation may be continued at Steps S109-S111, without beinginterrupted due to the inflation of the cuff 110.

[0135] Referring to FIGS. 19 and 20, there will be described a fifthembodiment of the present invention. The fifth embodiment relates to acontinuous BP monitor 400 having the same hardware construction as thatof the second embodiment shown in FIG. 7. The same reference numerals asused in the second embodiment are used to designate the correspondingelements or parts of the third embodiment and the description thereof isomitted.

[0136] However, as shown in FIG. 19, the BP monitor 400 has differentfunctions from those of the BP monitor 100 as the second embodiment. Acontrol device 128 of the BP monitor 400 functions as a cuff-pressureregulating means 494 which increases a pressure of a cuff 110 up to apredetermined target pressure, P_(CMM), and holds the cuff pressure atthe target value P_(CMM). The control device 128 also functions as apulse-area calculating means 488 which calculates an area, S_(MM),defined by each of successive heartbeat-synchronous pulses of a PPWsignal SM₂ which is obtained by a PPW sensor 146 when the cuff pressureis held at the target value P_(CMM) by the cuff-pressure regulatingmeans 494. The control device 128 also functions as a judging means 496which judges whether a MBP-P_(M) relationship determined by arelationship determining means 174 is accurate, based on one or morepulse areas S_(MM) calculated by the pulse-area calculating means 488.

[0137]FIG. 20 shows a flow chart representing a control programaccording to which the control device 128 controls the operation of thepresent BP monitor 400. The flow chart of FIG. 20 is different from thatof FIG. 11 in that in FIG. 20, Step S324 is inserted between Steps S102and S103 of FIG. 11 and Steps S435, S436, and S437 replace Steps S104,S105, and S106 of FIG. 11. Step S324 of FIG. 20 is the same as Step S324of FIG. 18, i.e., is provided for calculating an initial pulse area S₀.At Step S103, the increasing of the cuff pressure is started and, atStep S435, a CPU 129 of the control device 128 judges whether the cuffpressure has reached a predetermined target value P_(CMM). For example,the target value is predetermined to be higher than the last mean BPvalue MBP_(MEAN) determined at Step S111, by an excess value, β, of,e.g., 5 to 10 mmHg. Steps S103 and S435 correspond to the cuff-pressureregulating means 494.

[0138] At an early stage, negative judgments are made at Step S435.Meanwhile, a positive judgment is made at Step S435 while Steps S103 andS435 are repeated. Then, the cuff pressure is held at the target valueP_(CMM) and the control goes to Step S436 to calculate an area S_(MM) ofeach of heartbeat-synchronous pulses of the PPW signal SM₂ produced bythe PPW sensor 146 while the cuff pressure is maintained at the targetvalue P_(CMM). Step S436 corresponds to the pulse-area calculating means488. Step S436 is followed by Step S437 to judge whether a ratio,S_(MM)/S₀, of each pulse area S_(MM) to the initial pulse area S₀ is notgreater than a predetermined reference value, R_(MO). The referencevalue R_(MO) is predetermined such that in the case where the mean BPvalue of the patient plus the excess value β amounts to a value fallingwithin the range of the target value P_(CMM)±5 mmHg, the ratio S_(MM)/S₀is not greater than the reference value R_(MO).

[0139] If a positive judgment is made at Step S437, the currentMBP-P_(M) relationship is accurate and need not be updated. Therefore,the control of the CPU 129 skips Steps S107 and S108 and goes to StepS109 and the following steps to continue the continuous BP monitoringroutine. On the other hand, if a negative judgment is made at Step S437,the control goes to Steps S107 and S108 to carry out an oscillometric BPmeasurement and determine a new MBP-P_(M) relationship and subsequentlyresumes the continuous BP monitoring routine.

[0140] As is apparent from the foregoing description relating to thefifth embodiment shown in FIGS. 19 and 20, the CPU 129 of the controldevice 128 calculates, at Step S436, an area S_(MM) of each ofheartbeat-synchronous pulses of the PPW signal SM₂ obtained by the PPWsensor 146 while the cuff pressure is held at the target value P_(CMM)at Step S435. At Step S437, the CPU 129 judges whether the currentMBP-P_(M) relationship determined at Step S108 is accurate, based on theratio S_(MM)/S₀ of each pulse area S_(MM) to the initial pulse area S₀.If a positive judgment is made at Step S437, an oscillometric BPmeasuring operation is not carried out at step S107 and the currentrelationship is maintained without being updated at Step S108. Thus, thepatient is prevented from being pressed by the cuff 110. In addition,although the PPW sensor 146 is worn at a position downstream of the cuff110, a continuous BP monitoring operation may be continued at StepsS109-S111, without being interrupted due to the inflation of the cuff110.

[0141] In the third embodiment shown in FIGS. 13-16, the BP monitor 200may additionally include an exclusive cuff pulse wave (CPW) sensor 502as shown in FIG. 21. In this sixth embodiment, the CPW sensor 502 is seton a wrist 500 different from a wrist 142 on which the PPW sensor 146 isset. The CPW sensor 502 includes a belt 504 which is adapted to be woundaround the wrist 500, and a small inflatable bag 506 which is secured toan inner surface of the belt 504 and is inflatable inwardly. In use, theCPW sensor 502 is set on the wrist 500 such that the bag 506 ispositioned right above a radial artery located between a tendon and aradius bone in the wrist 500. In this case, the bag 506 canadvantageously press, when being inflated, the radial artery withoutbeing interfered with by the tendon and/or the radius. An air-supplydevice and a pressure sensor (not shown) are connected to the bag 506.

[0142] In each of the second to fifth embodiments, the BP measuringdevice 172 performs, at Step S107, an oscillometric BP measuring methodin which one or more BP values are determined based on the variation ofrespective amplitudes of heartbeat-synchronous pulses of the cuff pulsewave (i.e., CPW signal SM₁) obtained while the cuff pressure is changed.However, it is possible to employ, in place of the oscillometric method,a Korotkoff-sound method in which one or more BP values are determinedbased on the first detection and/or last detection (i.e., disappearance)of Korotkoff sounds detected by a microphone while the cuff pressure ischanged.

[0143] While in each of the second to sixth embodiments the judgingmeans 182, 286, 392, 496 uses only the last diastolic or mean BP valueMBP_(DIA), MBP_(MEAN) determined by the monitor-BP determining means176, for evaluating the accuracy of the MBP-P_(M) relationship, it ispossible to use, for the same purpose, an average of a plurality of lastdiastolic or mean BP values MBP_(DIA), MBP_(MEAN) determined based on aplurality of last pulses detected by the PPW sensor 146. In the lattercase, even if an abnormal lower-peak or mean magnitude of a PPW pulsemay be detected due to, e.g., a physical motion of the patient, theadverse influence of that magnitude to the judgment of the judging means182, 286, 392, 496 is effectively reduced.

[0144] Although in each of the second to sixth embodiments thecalibration of the MBP-P_(M) relationship is carried out at Steps S107and S108 at the predetermined period employed at Step S112, it ispossible to replace Step S112 by a step where the CPU 129 judges whethermonitor BP values MBP determined by the BP determining means 176 haveabnormally changed. In the latter case, if a positive judgment is madeat that step, the control of the CPU 129 goes back to Step S102.

[0145] Referring next to FIGS. 22 through 25, there will be described aseventh embodiment of the present invention. The seventh embodimentrelates to a continuous BP monitor 600 having the same hardwareconstruction as that of the second embodiment shown in FIG. 7. The samereference numerals as used in the second embodiment are used todesignate the corresponding elements or parts of the seventh embodimentand the description thereof is omitted.

[0146] However, as shown in FIG. 22, the BP monitor 600 has differentfunctions from those of the BP monitor 100 as the second embodiment. Acontrol device 128 of the BP monitor 600 functions as a firstpeak-interval determining means 680 which determines a first interval,D_(i) (FIG. 23), between an upper-peak point and a lower-peak point ofeach of successive heartbeat-synchronous pulses of a distal pulse wave,i.e., PPW signal SM₂ which is detected by a PPW sensor 146 when thepressure of an inflatable cuff 110 is increased at a predetermined rateby a cuff-pressure increasing means 178; as a second peak-intervaldetermining means 682 which determines a second interval, d_(i), betweenan upper-peak point and a lower-peak point of each of successiveheartbeat-synchronous pulses of a cuff pulse wave, i.e., CPW signal SM₁which is detected by a cuff pulse wave sensor 114, 124, 130 including apulse-wave filter circuit 124, when the pressure of the cuff 110 isincreased at the predetermined rate by the cuff-pressure increasingmeans 178; as a difference determining means 684 which determines adifference between the first interval of each of the successiveheartbeat-synchronous pulses of the pressure pulse wave (PPW) and thesecond interval of a corresponding one of the successiveheartbeat-synchronous pulses of the cuff pulse wave (CPW); and a judgingmeans 686 which judges whether the relationship determined by arelationship determining means 174 is accurate, based on one or morediastolic BP values MBP_(DIA) determined by a monitor-BP determiningmeans 176 and a cuff pressure corresponding to a point, K₃ (FIG. 25), ortime when the differences determined by the difference determining means684 significantly largely change.

[0147]FIG. 24 shows a flow chart representing a control programaccording to which the control device 128 controls the operation of thepresent BP monitor 600. The flow chart of FIG. 24 is different from thatof FIG. 11 in that Step S104 of FIG. 11 is replaced by Steps S604, S605,and S606 of FIG. 24.

[0148] At Step S103, a CPU 129 of the control device 128 controls thecuff-pressure increasing means 178 to start increasing the cuff pressurefrom atmospheric pressure at a predetermined rate of, e.g., 5 to 20mmHg/sec. At Step S604, first, the PPW sensor 146 and the CPW sensor114, 124, 130 obtain the PPW signal SM₂ and the CPW signal SM₁ as shownin a top and a bottom of the graph of FIG. 23, respectively, and the CPU129 determines a time interval D_(i) (i=1, 2, . . . ) between anupper-peak point, P_(M2max), and a lower-peak point, P_(M2min), of eachof successive heartbeat-synchronous pulses of the PPW and a timeinterval d_(i) (i=1, 2, . . . ) between an upper-peak point, P_(M1max),and a lower-peak point, P_(M1min), of each of successiveheartbeat-synchronous pulses of the CPW. Step S604 corresponds to thefirst and second peak-interval determining means 680, 682.

[0149] Step S604 is followed by Step S605 to calculate a difference,t_(i) (=d_(i)−D_(i), msec), between the first interval D_(i) of each ofthe heartbeat-synchronous pulses of the PPW and the second intervald_(i) of a corresponding one of the heartbeat-synchronous pulses of theCPW which is produced in synchronism with that each pulse of the PPW inresponse to the same heartbeat. Step S605 corresponds to the differencedetermining means 684. Step S605 is followed by Step S606 to judgewhether the CPU 129 has identified a time when the differences ti havesignificantly largely changed. For example, the CPU 129 differentiatesthe difference values t_(i) and determines a point, K₃, corresponding tothe greatest differential, as illustrated in FIG. 25. When the cuffpressure takes values between the systolic and diastolic BP values ofthe patient, the lower-peak portion of the waveform of each pulse of thePPW signal SM₂ is cut off. The point K₃ is indicative of a time when thecuff pressure is equal to an actual diastolic BP value of the patient.If a positive judgment is made at Step S606, the control goes to StepS105 to determine a cuff pressure P_(CD1) corresponding to the point K₃identified at Step S606 and store it in a RAM 133. Thus, the cuffpressure P_(CD1) is indicative of an actual diastolic BP value of thepatient. In the present embodiment, Step S105 corresponds to a diastolicpressure determining means.

[0150] Step S105 is followed by Step S106 to judge whether the currentMBP-P_(M) relationship determined at Step S108 is accurate orappropriate, based on the last diastolic BP value MBP_(DIA) determinedat Step S111 and the cuff pressure P_(CD1) stored at Step S105. Forexample, the CPU 129 judges whether the absolute value of the differenceof the last diastolic BP value MBP_(DIA)and the cuff pressure P_(CD1),i.e., |MBP_(DIA)−P_(CD1)|, is not greater than a reference value, ΔP₁.This reference value is, e.g., 5 mmHg. Step S106 corresponds to thejudging means 686.

[0151] As is apparent from the foregoing description relating to theseventh embodiment shown in FIGS. 22 to 25, the CPU 129 of the controldevice 128 determines, at Step S604, a time interval D_(i) between anupper-peak point P_(M2max) and a lower-peak point P_(M2min) of each ofsuccessive heartbeat-synchronous pulses of the PPW and a time intervald_(i) between an upper-peak point P_(M1max) and a lower-peak pointP_(M1min) of each of successive heartbeat-synchronous pulses of the CPW.The PPW and the CPW are detected by the PPW sensor 146 and the CPWsensor 114, 124, 130, respectively, when the cuff pressure is increasedat a predetermined rate at Step S103. At Step S605, the CPU 129calculates a peak-interval difference t_(i) between the first intervalD_(i) of each of the heartbeat-synchronous pulses of the PPW and thesecond interval d_(i) of a corresponding one of theheartbeat-synchronous pulses of the CPW which is produced in synchronismwith that each pulse of the PPW in response to the same heartbeat. AtStep S105, the CPU 129 determines, as a diastolic BP value of thepatient, a cuff pressure P_(CD1) corresponding to the point K₃ isidentified at Step S606. At Step S106, the CPU 129 judges whether theMBP-P_(M) relationship determined at Step S108 is accurate, based on thelast diastolic BP value MBP_(DIA) determined at Step S111 and the cuffpressure P_(CD1) stored at Step S105.

[0152] If a positive judgment is made at Step S106, an oscillometric BPmeasuring operation is not carried out at Step S107 and the currentrelationship is maintained without being updated at Step S108. Thus, thepatient is prevented from being pressed by the cuff 110. In addition,although the PPW sensor 146 is worn at a position downstream of the cuff110, a continuous BP monitoring operation may be continued at StepsS109-S111, without being interrupted due to the inflation of the cuff110.

[0153] In the seventh embodiment, the upper-peak and lower-peak pointsof each pulse of the CPW are not influenced by the increasing of thecuff pressure, whereas the upper-peak and lower-peak points of eachpulse of the PPW are influenced by the increasing of the cuff pressure,as shown in FIG. 23, because the PPW sensor 146 is set on the distalside of the cuff 110. Therefore, the peak-interval differences t_(i) areinfluenced by the increasing of the cuff pressure. Thus, a cuff pressurecorresponding to the point K₃ where the differences t_(i) significantlylargely change, is equal to a diastolic BP value of the patient.Accordingly, the accuracy of the MBP-P_(M) relationship can be judged byincreasing the cuff pressure up to a value around the diastolic BP valueof the patient, which does not cause the patient to feel discomfort. Inaddition, in the case where a physiological change such as arrhythmiaoccurs to the heart of the patient, respective waveforms of the CPW andthe PPW change in a similar manner, so that the peak-intervaldifferences t_(i) are not influenced by this change. Thus, the accuracyof the MBP-P_(M) relationship can be judged with high reliability.

[0154] In the seventh embodiment, since the judgment about whether theMBP-P_(M) relationship is accurate is made based on the cuff pressureP_(CD1) and the last diastolic BP value MBP_(DIA) determined at StepS111, it is more accurate than a judgment made based on a diastolic BPvalue MBP_(DIA) determined at Step S111 a predetermined time before, orthe last diastolic BP value BP_(DIA) measured at Step S107.

[0155] Referring next to FIGS. 26 through 28, there will be described aneighth embodiment of the present invention. The eighth embodimentrelates to a BP monitor 700 having a hardware construction basicallysimilar to that of the second embodiment shown in FIG. 7 and including aphotoelectric pulse wave detecting probe 788 in place of the PPWdetecting probe 134 of the second embodiment. The same referencenumerals as used in the second embodiment are used to designate thecorresponding elements or parts of the eighth embodiment and thedescription thereof is omitted.

[0156] The probe 788 is held, with the help of a band (not shown), inclose contact with a body surface 138 of a wrist 142 of a patientlocated on a distal side of an inflatable cuff 110 being wound around anupper arm 112 of so the patient. The probe 788 includes a container-likecylindrical housing 792 having a circular bottom wall and a circularopening; a plurality of first light emitting elements 794 a (e.g., lightemitting diodes (LEDs)) and a plurality of second light emittingelements 794 b which are secured to an outer annular portion of thebottom wall of the housing 792; a light detecting element (e.g., photodiode or photo transistor) which is secured to a central portion of thebottom wall of the housing 792; a transparent resin 798 which covers thelight emitting elements 794 (794 a, 794 b) and the light detectingelement 796 and fills the spaces left in the housing 792; and acylindrical light-shading member 800 which prevents the lights emittedfrom the light emitting members 794 and reflected by the body surface138, from being received by the light detecting element 796.

[0157] The first light emitting elements 794 a emit a red light having,e.g., a 660 nm wavelength, and the second light emitting elements 794 bemit an infra-red light having, e.g., a 800 nm wavelength. Various pairsof lights each pair of which have different wavelengths may be employedin place of the 660 nm and 800 nm wavelength lights, so long as onelight of each pair exhibits significantly different absorption factorswith respect to hemoglobin and oxygenated hemoglobin, respectively, andthe other light exhibits substantially the same absorption factors withrespect to the two sorts of hemoglobin, respectively. The first lightemitting elements 794 a and the second light emitting elements 794 balternately and periodically emit the red and infrared lights,respectively, such that each light emission lasts a predetermined, veryshort duration of time. The red and infrared lights emitted from thefirst and second light emitting elements 794 a, 794 b are reflected froma blood-vessel bed under the body surface 138, and the reflected lightsare detected by the common light detecting element 796.

[0158] The light detector 796 generates a photoelectric pulse wavesignal (electric signal), SM₃, whose magnitude corresponds to thedetected intensity of a reflected red or infrared light, to a low-passfilter 802 via an amplifier (not shown). The magnitude of the signal SM₃is variable because of the pulsation of blood in the blood vessels underthe boay surface 138. The low-pass filter 802 clears the signal SM₃ ofnoise whose frequencies are higher than the frequency of the bloodpulsation, and supplies the cleared signal SM₃ to a demultiplexer 804.The demultiplexer 804 is selectively placed in a first and a secondstate thereof according to a switch signal, SC, (described below),supplied from a control device 128, in synchronism with the alternateand periodic light emissions from the first and second light emitters794 a, 794 b. More specifically described, when the first light emitters794 a emit a red light, the demultiplexer 804 is placed in the firststate in which the demultiplexer 804 permits an electric signal, SM_(R),representing the detected intensity of the reflected red light, to besupplied to an input and output (I/O) port (not shown) of the controldevice 128 via a first sample-hold circuit 806 and a third A/D converter158; and when the second light emitters 794 b emit an infrared light,the demultiplexer 804 is placed in the second state in which thedemultiplexer 804 permits an electric signal, SM_(IR), representing thedetected intensity of the reflected infrared light, to be supplied tothe I/O port of the control device 128 via a second sample-hold circuit808 and a fourth A/D converter 810. The first and second sample-holdcircuits 806, 808 supply the signals SM_(R), SM_(IR) to the third andfourth A/D converters 158, 810, respectively, such that the circuits806, 808 continue to hold the signals SM_(R), SM_(IR) received in acurrent cycle until the converters 158, 810 complete the respectiveanalog to digital conversions of the signals SM_(R), SM_(IR) which inthe preceding cycle the circuits 806, 808 have supplied to theconverters 158, 810, respectively. In the present embodiment, thephotoelectric pulse wave detecting probe 788 provides a distal pulsewave sensor which is adapted to be set on the distal side of the cuff110.

[0159] In the present embodiment, a first and a second A/D converter126, 130, a display 132, etc. are connected to the control device 128,like in the second embodiment shown in FIG. 7. However, the second airpump 150 or the pressure regulator valve 152 is not employed.

[0160] A CPU 129 of the control device 128 generates a light-emissioncontrol signal, SLV, to a drive circuit 812 so that the first and secondlight emitters 794 a, 794 b alternately and periodically emit the redand infrared lights, respectively. In synchronism with the alternate andperiodic light emissions from the first and second light emitters 794 a,794 b, the CPU 129 generates the switch signal SC to the demultiplexer804 so as to place correspondingly the demultiplexer 804 in the first orsecond state. Thus, the photoelectric pulse wave signal SM₃ is separatedby the demultiplexer 804 such that the red-light signal SM_(R) issupplied to the first sample-hold circuit 806 and the infrared-lightsignal SM_(IR) is supplied to the second sample-hold circuit 808.

[0161] In addition, the CPU 129 processes the input signals SM_(R),SM_(IR) supplied from the third and fourth A/D converters 158, 810,according to a control program pre-stored in a ROM 131, and determinesan oxygen saturation of the blood flowing through the blood vesselsunder the body surface 138, based on the respective waveforms of thesignals SM_(R), SM_(IR). The CPU 129 commands the display 132 to displaythe determined blood oxygen saturation. The manner of determination ofthe blood oxygen saturation employed in the present embodiment is thesame as that disclosed in, e.g., U.S. Pat. No. 5,131,391 assigned to theAssignee of the present application. The disclosure of this patent isincorporated herein by reference. In short, the CPU 129 determines ablood oxygen saturation of a patient based on a ratio, A/B, according toa predetermined relationship between ratio A/B and blood oxygensaturation, where A=(V_(dR)−V_(sR))/(V_(dR)+V_(sR)), andB=(V_(dIR)−V_(sIR))/(V_(dIR)+V_(sIR)). The signal SM₃ has a waveformsimilar to that shown in the top of the graph of FIG. 23. The valuesV_(dR), V_(sR) are an upper-peak and a lower-peak magnitude of eachpulse of the red-light signal SM_(R), and the values V_(dIR), V_(sIR)are an upper-peak and a lower-peak magnitude of each pulse of theinfrared-light signal SM_(IR).

[0162] As shown in FIG. 27, the BP monitor 700 has different functionsfrom those of the BP monitor 100 as the second embodiment. A controldevice 128 of the BP monitor 700 functions as a second peak-intervaldetermining means 682 that is the same as the means 682 of the BPmonitor 600 shown in FIG. 22. The second peak-interval determining means682 determines a second interval between an upper-peak point and alower-peak point of each pulse of a CPW signal SM₁ supplied from apulse-wave filter circuit 124.

[0163] The CPU 129 also functions as an oxygen-saturation determiningmeans 814 which determines a blood oxygen saturation of a patient basedon the photoelectric pulse wave signal SM₃ supplied from the probe 788.Moreover, the CPU 129 functions as a first peak-interval determiningmeans 780 which determines a first interval between an upper-peak pointand a lower-peak point of each pulse of the signal SM₃; and a differencedetermining means 784 which determines a difference, t, between thefirst interval of each of the successive heartbeat-synchronous pulse ofthe photoelectric pulse wave and the second interval of a correspondingone of the successive heartbeat-synchronous pulses of the cuff pulsewave; and a diastolic-pressure determining means 816 which determines,as a diastolic pressure of the patient, a cuff pressure CD1corresponding to a point K₃ or time when the differences t determined bythe difference determining means 784 significantly largely change.

[0164]FIG. 28 shows a flow chart representing a control programaccording to which the control device 128 controls the operation of thepresent BP monitor 700. Steps S103 and Step S107 of the flow chart ofFIG. 28 are the same as Steps S103 and Step S107 of the flow chart ofFIG. 11, and Steps S604, S605, and S606 of the flow chart of FIG. 28 arethe same as Steps S604, S605, and Step S606 of the flow chart of FIG.24, and the description of those steps is omitted, if appropriate.

[0165] Initially, at Step S715, the CPU 129 reads in eachheartbeat-synchronous pulse of the red-light signal SM_(R) and eachheartbeat-synchronous pulse of the infra-red signal SM_(IR), from thephotoelectric pulse wave detecting probe 788. On one hand, those pulsesare used for determining a blood oxygen saturation of the patient asdescribed above and, on the other hand, the same pulses are processedaccording to Step S716 and the following steps of the flow chart of FIG.28.

[0166] At Step S716, the CPU 129 judges whether a predetermined firstperiod has passed after a diastolic pressure BP_(DIA) is determined atStep S717 in the preceding control cycle. The first period may bepredetermined (e.g., selected) at an appropriate time by an operator. Ifa negative judgment is made at Step S716, the control of the CPU 129goes back to Step S715 to read in the signals SM_(R), SM_(IR).Meanwhile, if a positive judgment is made at Step S716, the control ofthe CPU 129 proceeds with Steps S103, S604, S605, and S606 that are thesame as Steps S103, S604, S605, and S606 of the flow chart of FIG. 24,except that in the eighth embodiment the signal SM₃ (SM_(R) or SM_(IR))is employed in place of the PPW signal SM₂.

[0167] If a point K₃ is identified as shown in FIG. 25 and a positivejudgment is made at Step S606, the control of the CPU 129 goes to StepS717 to determine, as a diastolic pressure BP_(DIA) of the patient, acuff pressure P_(CD1) corresponding to the point K₃, i.e., time when thepeak-interval differences t_(i) determined at Step S605 significantlylargely change. Step S717 is followed by Step S718 to command thedisplay 132 to display the determined diastolic pressure BP_(DIA).

[0168] Subsequently, the control of the CPU 129 goes to Step S719 tojudge whether the diastolic-pressure value BP_(DIA) determined at StepS718 in the current control cycle is higher than a reference value whichis predetermined to be higher by an excess value than a moving averageof a predetermined number of prior diastolic-pressure values BP_(DIA)determined in the same number of prior control cycles. If a positivejudgment is made at Step S719, the control goes to Step S720 to commandthe display 132 to display an informing message that the diastolicpressure BP_(DIA) of the patient is abnormal. On the other hand, if anegative judgment is made at Step S719, the control goes back to StepS715. Step S720 is followed by Step S721 to judge whether a secondpredetermined period has passed after a systolic, a mean, and adiastolic BP value BP_(SYS), BP_(MEAN), BP_(DIA) are measured using thecuff 110 according to the oscillometric method, at Step S107 in theprior control cycle. The second period may be predetermined independentof the first period. However, the second period is predetermined to benot shorter than the shortest BP measurement period (2 minutes and 30seconds) specified by WHO (World Health Organization). If a negativejudgment is made at Step S721, the control goes back to Step S715 sothat another diastolic pressure can be measured while the display 132continues to display the “abnormality” message. On the other hand, if apositive judgment is made at Step S721, the control goes to Step S107 tocontinue to increase the cuff pressure so that BP values BP_(SYS),BP_(MEAN), BP_(DIA) are measured according to the oscillometric method.Then, the control of the CPU 129 goes back to Step S715.

[0169] As is apparent from the foregoing description relating to theeighth embodiment shown in FIGS. 26 to 28, the CPU 129 of the controldevice 128 determines, at Step S605, a time interval D_(i) between anupper-peak point V_(sR) or V_(sIR) and a lower-peak point V_(dR) orV_(dIR) of each of successive heartbeat-synchronous pulses of thered-light or infrared-light signal SM_(R) or SM_(IR) and a time intervald_(i) between an upper-peak point P_(M1max) and a lower-peak pointP_(M1min) of each of successive heartbeat-synchronous pulses of the CPWsignal SM₁. The signal SM_(R) or SM_(IR) and the signal SM₁ are detectedby the probe 788 and the CPW sensor 114, 124, 130 respectively, when thecuff pressure is increased at a predetermined rate at Step S103. At StepS605, the CPU 129 calculates a peak-interval difference t_(i) betweenthe first interval D_(i) of each of the heartbeat-synchronous pulses ofthe signal SM_(R) or SM_(IR) and the second interval d_(i) of acorresponding one of the heartbeat-synchronous pulses of the CPW signalSM₁ which is produced in synchronism with that each pulse of the signalSM_(R) or SM_(IR) in response to the same heartbeat. At Step S606, theCPU 129 identifies a point K₃ where the rate of change of thepeak-interval differences t_(i) significahtly largely change. At StepS717, the CPU 129 determines, as a diastolic BP value BP_(DIA) of thepatient, a cuff pressure P_(CD1) corresponding to the point K₃identified at Step S606, and commands the display 132 to display thedetermined diastolic pressure BP_(DIA). At Step S719, the CPU 129 judgeswhether the diastolic-pressure value BP_(DIA) is abnormal, based on theamount of change of it from the prior diastolic-pressure valuesBP_(DIA).

[0170] If a negative judgment is made at Step S719, an oscillometric BPmeasuring operation is not carried out at Step S107. Thus, the presentBP monitor 700 can monitor the blood pressure of the patient withoutcausing the patient to feel the discomfort due to highly frequentpressing of the cuff 110. In the present embodiment, the photoelectricpulse wave detecting probe 788 is used for not only monitoring the bloodoxygen saturation of the patient but also the blood pressure of thepatient. Thus, the total number of sensors which are worn on the patientis reduced as compared with the case where an exclusive distal pulsewave sensor is employed.

[0171] Although the probe 788 is worn at a position downstream of thecuff 110, a continuous blood oxygen saturation monitoring operationusing the probe 788 may be continued without being interrupted due tothe inflation of the cuff 110 at Step S103, because in a continuous BPmonitoring operation the cuff pressure is not increased to values higherthan the diastolic pressure of the patient.

[0172] When the display 132 informs the operator of the abnormal changeof the diastolic pressure BP_(DIA) of the patient, he or she can take anappropriate action against it. Even in this case, the oscillometric BPmeasurement is not carried out at Step S107, before the secondpredetermined period has-passed at Step S721. Therefore, the patient isprevented from being highly frequently pressed by the cuff 110.

[0173] In each of the seventh and eighth embodiments, the BP measuringdevice 172 performs, at Step S107, an oscillometric BP measuring methodin which one or more BP values are determined based on the variation ofrespective amplitudes of heartbeat-synchronous pulses of the cuff pulsewave (i.e., CPW signal SM₁) obtained while the cuff pressure is changed.However, it is possible to employ, in place of the oscillometric method,a Korotkoff-sound method in which one or more BP values are determinedbased on the first detection and/or last detection (i.e., disappearance)of Korotkoff sounds detected by a microphone while the cuff pressure ischanged.

[0174] While in the seventh embodiment the judging means 686 uses onlythe last diastolic BP value MBP_(DIA) determined by the monitor-BPdetermining means 176, for evaluating the accuracy of the MBP-P_(M)relationship, it is possible to use, for the same purpose, an average ofa plurality of last diastolic BP values MBP_(DIA) determined based on aplurality of last pulses detected by the PPW sensor 146. In the lattercase, even if an abnormal lower-peak magnitude of a PPW pulse may bedetected due to, e.g., a physical motion of the patient, the adverseinfluence of that magnitude to the judgment of the judging means 686 iseffectively reduced.

[0175] Although in the seventh embodiment the calibration of theMBP-P_(M) relationship is carried out at Steps S107 and S108 at apredetermined period employed at Step S112, it is possible to replaceStep S112 by a step where the CPU 129 judges whether monitor BP valuesMBP determined by the BP determining means 176 have abnormally changed.In the latter case, if a positive judgment is made at that step, thenthe control of the CPU 129 goes back to Step S102.

[0176] While in each of the seventh and eighth embodiments the cuff 110is adapted to be wound around the upper arm 112 of the patient, it ispossible to employ an inflatable cuff which is adapted to be woundaround a different body portion of a patient such as a wrist.

[0177] In the eighth embodiment, it is possible to omit Step S107 fromthe flow chart of FIG. 28. In the latter case, if a positive judgment ismade at Step S719, the CPU 129 only commands, at Step S720, the display132 to display the “abnormality” message. Alternatively, it is possibleto omit Step S720 from the flow chart of FIG. 28. In the last case, if apositive judgment is made at Step S719, the CPU 129 is only able tocommand, at Step S107, the BP measuring device 172 to carry out anoscillometric BP measurement using the cuff 110. The reference valueemployed at Step S719 for finding an abnormal diastolic pressureBP_(DIA) may be predetermined in a manner other than described therein.

[0178] In the eighth embodiment, the first period used at Step S716 maybe predetermined to be longer than the second period used at Step S721.In the latter case, it is possible to omit Step S721. In the last case,whenever a positive judgment is made at Step S719, the CPU 129 commands,at Step S107, the BP measuring device 172 to carry out an oscillometricBP measurement using the cuff 110.

[0179] While in the eighth embodiment the reflection-type probe 788 thatdetects the lights reflected from the blood vessels under the bodysurface 138 of the patient is employed, it is possible to employ atransmission-type probe that detects the lights transmitted through thebody portion or tissue 142 of the patient.

[0180] In each of the seventh and eighth embodiments, the PPW sensor 146or the probe 788 may be replaced by a different sort of pulse wavesensor, e.g., an impedance sensor which detects the change of impedanceof a living subject due to blood pulsation and which is used in theso-called impedance plethysmography.

[0181] In the eighth embodiment, the probe 788 is employed formonitoring both the blood pressure and blood oxygen saturation of aliving subject. However, it is possible to employ, in place of the probe788, an exclusive sensor which detects a photoelectric pulse wave forexclusively monitoring the blood pressure of a living subject, or asensor which detects a photoelectric pulse wave for monitoring both theblood pressure and peripheral blood circulation of a living subject.

[0182] It is to be understood that the present invention may be embodiedwith other changes, improvements, and modifications that may occur tothose skilled in the art without departing from the spirit and scope ofthe invention defined in the appended claims.

What is claimed is:
 1. A blood pressure monitor comprising: aninflatable cuff which is adapted to be wound around a body portion of aliving subject to press said body portion; a pressure sensor whichdetects a pressure in said cuff; a cuff-pressure regulating device whichincreases the pressure of said cuff; pulse-amplitude determining meansfor determining an amplitude of each of pulses of a pulse wave which areproduced in said cuff and detected by said pressure sensor while thepressure of said cuff is increased by said cuff-pressure regulatingdevice; candidate determining means for determining, as a diastolicblood pressure candidate, a pressure of said cuff which is detected bysaid pressure sensor and which corresponds to an amplitude of a firstpulse of said pulses determined by said pulse-amplitude determiningmeans, by judging whether the amplitude of said first pulse is notgreater than a reference value which is smaller than an amplitude of atleast one second pulse of said pulses, by a predetermined proportion ofthe amplitude of said second pulse, the amplitude of said second pulsebeing determined by said pulse-amplitude determining means after theamplitude of said first pulse is determined; and blood-pressuredetermining means for determining, as a monitor diastolic blood pressurevalue, said pressure of said cuff corresponding to said amplitude ofsaid first pulse, when said candidate determining means determines, assaid diastolic blood pressure candidate, said pressure of said cuffcorresponding to said amplitude of said first pulse, with respect to apredetermined number of said at least one second pulse.
 2. A bloodpressure monitor according to claim 1, wherein said candidatedetermining means comprises judging means for judging whether theamplitude of said first pulse is not greater than a reference valuewhich is smaller than an amplitude of each of a plurality of secondpulses of said pulses, by a predetermined proportion of the amplitude ofsaid each second pulse, the respective amplitudes of said second pulsesbeing determined by said pulse-amplitude determining means after theamplitude of said first pulse is determined.
 3. A blood pressure monitoraccording to claim 1, wherein said cuff-pressure regulating devicecomprises pressure increasing means for stepwise increasing the pressureof said cuff by alternately increasing the cuff pressure and maintainingthe cuff pressure at each of a plurality of different pressure values,and wherein said pulse-amplitude determining means determines anamplitude of at least one pulse which is produced in said cuff anddetected by said pressure sensor while the cuff pressure is maintainedat said each pressure value.
 4. A blood pressure monitor according toclaim 1, wherein said blood-pressure determining means comprises monitormeans for iteratively determining said monitor diastolic blood pressurevalue.
 5. A blood pressure monitor according to claim 4, furthercomprising abnormality identifying means for identifying an abnormalityof the monitor diastolic blood pressure values iteratively determined bysaid monitor means.
 6. A blood pressure monitor according to claim 5,wherein said abnormality identifying means comprises means foridentifying said abnormality based on at least one of an amount ofchange of a last determined value of said monitor diastolic bloodpressure values from an average of said monitor diastolic blood pressurevalues, and a rate of change of said last determined value of saidmonitor diastolic blood pressure values from said average of saidmonitor diastolic blood pressure values.
 7. A blood pressure monitoraccording to claim 5, further comprising a blood pressure measuringdevice which increases the pressure of said cuff up to a target pressurewhich is higher than a systolic blood pressure of the subject andmeasures at least one of a systolic, a mean, and a diastolic bloodpressure value of the living subject based on a variation of respectiveamplitudes of pulses of a pulse wave which are produced in said cuff anddetected by said pressure sensor during at least one of the increasingof the cuff pressure up to said target pressure and a decreasing of thecuff pressure down from said target pressure.
 8. A blood pressuremonitor according to claim 7, wherein said blood pressure measuringdevice comprises means for measuring said at least one of said systolic,said mean, and said diastolic blood pressure value of the living subjectwhen said abnormality identifying means identifies said abnormality. 9.A blood pressure monitor according to claim 1, further comprising adisplay which displays said monitor diastolic blood pressure valuedetermined by said blood-pressure determining means.
 10. A bloodpressure monitor according to claim 1, wherein said predeterminedproportion is 0.3.
 11. A blood pressure monitor according to claim 1,wherein said predetermined number is three.
 12. A blood pressure monitorcomprising: an inflatable cuff which is adapted to be wound around abody portion of a living subject to press said body portion throughwhich an artery of the subject extends; a blood pressure measuringdevice which measures a blood pressure of the subject by changing apressure in said cuff; a pressure pulse wave sensor which is adapted tobe pressed against a distal section of said artery located on a distalside of said cuff wound around said body portion, so as to detect apressure pulse wave which is produced from said distal section of theartery and is propagated thereto via a skin tissue above said distalsection; relationship determining means for determining a relationshipbetween blood pressure and magnitude of pressure pulse wave, based onthe blood pressure measured by said blood pressure measuring device anda magnitude of the pressure pulse wave detected by said pressure pulsewave sensor; blood pressure determining means for successivelydetermining at least a diastolic blood pressure of the subject accordingto the determined relationship based on a magnitude of a lower-peakpoint of each of successive first heartbeat-synchronous pulses of saidpressure pulse wave detected by said pressure pulse wave sensor;cuff-pressure increasing means for increasing said pressure of said cuffat a predetermined rate; waveform-characteristic determining means fordetermining a characteristic of a lower-peak portion of a waveform ofeach of successive second heartbeat-synchronous pulses of said pressurepulse wave which are detected by said pressure pulse wave sensor whensaid pressure of said cuff is increased at said predetermined rate bysaid cuff-pressure increasing means, said lower-peak portion including alower-peak point of said each second heartbeat-synchronous pulse; andjudging means for judging whether said determined relationship isaccurate, based on at least one diastolic blood pressure determined bysaid blood pressure determining means and a pressure of said cuffcorresponding to a time when the waveform characteristics determined bysaid waveform-characteristic determining means significantly largelychange.
 13. A blood pressure monitor comprising: an inflatable cuffwhich is adapted to be wound around a body portion of a living subjectto press said body portion through which an artery of the subjectextends; a blood pressure measuring device which measures a bloodpressure of the subject by changing a pressure in said cuff; a pressurepulse wave sensor which is adapted to be pressed against a distalsection of said artery located on a distal side of said cuff woundaround said body portion, so as to detect a pressure pulse wave which isproduced from said distal section of the artery and is propagatedthereto via a skin tissue above said distal section; relationshipdetermining means for determining a relationship between blood pressureand magnitude of pressure pulse wave, based on the blood pressuremeasured by said blood pressure measuring device and a magnitude of thepressure pulse wave detected by said pressure pulse wave sensor; bloodpressure determining means for determining at least a diastolic bloodpressure of the subject according to the determined relationship basedon a magnitude of a lower-peak point of each of successive firstheartbeat-synchronous pulses of said pressure pulse wave detected bysaid pressure pulse wave sensor; cuff-pressure increasing means forincreasing said pressure of said cuff at a predetermined rate; a cuffpulse wave sensor which detects a cuff pulse wave which is a pressureoscillation produced in said cuff; phase-difference determining meansfor determining a phase difference of respective lower-peak points ofeach of successive second heartbeat-synchronous pulses of said pressurepulse wave and a corresponding one of successive heartbeat-synchronouspulses of said cuff pulse wave, said second heartbeat-synchronous pulsesof said pressure pulse wave and said heartbeat-synchronous pulses ofsaid cuff pulse wave being detected by said pressure pulse wave sensorand said cuff pulse wave sensor, respectively, when said pressure ofsaid cuff is increased at said predetermined rate by said cuff-pressureincreasing means; and judging means for judging whether said determinedrelationship is accurate, based on at least one diastolic blood pressuredetermined by said blood pressure determining means and a pressure ofsaid cuff corresponding to a time when the phase differences determinedby said phase-difference determining means significantly largely change.14. A blood pressure monitor comprising: an inflatable cuff which isadapted to be wound around a body portion of a living subject to presssaid body portion through which an artery of the subject extends; ablood pressure measuring device which measures a blood pressure of thesubject by changing a pressure in said cuff; a pressure pulse wavesensor which is adapted to be pressed against a distal section of saidartery located on a distal side of said cuff wound around said bodyportion, so as to detect a pressure pulse wave which is produced fromsaid distal section of the artery and is propagated thereto via a skintissue above said distal section; relationship determining means fordetermining a relationship between blood pressure and magnitude ofpressure pulse wave, based on the blood pressure measured by said bloodpressure measuring device and a magnitude of the pressure pulse wavedetected by said pressure pulse wave sensor; blood pressure determiningmeans for determining at least a mean blood pressure of the subjectaccording to the determined relationship based on a mean magnitude ofeach of successive first heartbeat-synchronous pulses of said pressurepulse wave detected by said pressure pulse wave sensor; cuff-pressureincreasing means for increasing said pressure of said cuff at apredetermined rate; pulse-area calculating means for calculating an areadefined by each of successive second heartbeat-synchronous pulses ofsaid pressure pulse wave which are detected by said pressure pulse wavesensor when said pressure of said cuff is increased at saidpredetermined rate by said cuff-pressure increasing means; half-areaidentifying means for identifying that the pulse areas calculated bysaid pulse-area calculating means have decreased to half an initialpulse area obtained before said cuff-pressure increasing means startsincreasing said pressure of said cuff; and judging means for judgingwhether said determined relationship is accurate, based on at least onemean blood pressure determined by said blood pressure determining meansand a pressure of said cuff corresponding to a time when said half-areaidentifying means identifies that the pulse areas calculated by saidpulse-area calculating means have decreased to half said initial pulsearea.
 15. A blood pressure monitor comprising: an inflatable cuff whichis adapted to be wound around a body portion of a living subject topress said body portion through which an artery of the subject extends;a blood pressure measuring device which measures a blood pressure of thesubject by changing a pressure in said cuff; a pressure pulse wavesensor which is adapted to be pressed against a distal section of saidartery located on a distal side of said cuff wound around said bodyportion, so as to detect a pressure pulse wave which is produced fromsaid distal section of the artery and is propagated thereto via a skintissue above said distal section; relationship determining means fordetermining a relationship between blood pressure and magnitude ofpressure pulse wave, based on the blood pressure measured by said bloodpressure measuring device and a magnitude of the pressure pulse wavedetected by said pressure pulse wave sensor; blood pressure determiningmeans for determining a blood pressure of the subject according to thedetermined relationship based on a magnitude of each of successive firstheartbeat-synchronous pulses of said pressure pulse wave detected bysaid pressure pulse wave sensor; cuff-pressure regulating means forincreasing said pressure of said cuff up to a predetermined value andholding the cuff pressure at said predetermined value; pulse-areacalculating means for calculating an area defined by each of successivesecond heartbeat-synchronous pulses of said pressure pulse wave whichare detected by said pressure pulse wave sensor when said cuff pressureis held at said predetermined value by said cuff-pressure regulatingmeans; and judging means for judging whether said determinedrelationship is accurate, based on a ratio of the calculated area of atleast one said second heartbeat-synchronous pulse of said pressure pulsewave detected by said pressure pulse wave when said cuff pressure isheld at said predetermined value by said cuff-pressure regulating means,to an initial pulse area obtained before the cuff-pressure regulatingmeans starts increasing said cuff pressure.
 16. A blood pressure monitorcomprising: an inflatable cuff which is adapted to be wound around abody portion of a living subject to press said body portion throughwhich an artery of the subject extends; a blood pressure measuringdevice which measures a blood pressure of the subject by changing apressure in said cuff; a cuff pulse wave sensor which detects a cuffpulse wave which is a pressure oscillation produced in said cuff; adistal pulse wave sensor which detects a distal pulse wave from a distalsection of said artery located on a distal side of said cuff woundaround said body portion; cuff-pressure increasing means for increasingsaid pressure of said cuff at a predetermined rate; first peak-intervaldetermining means for determining a first interval between an upper-peakpoint and a lower-peak point of each of first heartbeat-synchronouspulses of said distal pulse wave which are detected by said distal pulsewave sensor when said pressure of said cuff is increased at saidpredetermined rate by said cuff-pressure increasing means; secondpeak-interval determining means for determining a second intervalbetween an upper-peak point and a lower-peak point of each of secondheartbeat-synchronous pulses of said cuff pulse wave which are detectedby said cuff pulse wave sensor when said pressure of said cuff isincreased at said predetermined rate by said cuff-pressure increasingmeans; difference determining means for determining a difference betweenthe first interval of said each of said first heartbeat-synchronouspulses and the second interval of a corresponding one of said secondheartbeat-synchronous pulses; and blood pressure determining means fordetermining, as a diastolic blood pressure of the subject, a pressure ofsaid cuff corresponding to a time when the differences determined bysaid difference determining means significantly largely change.
 17. Ablood pressure monitor according to claim 16, wherein said distal pulsesensor comprises a pressure pulse wave sensor which is adapted to bepressed against the distal section of the artery via a skin tissue abovethe distal section, so as to detect a pressure pulse wave which isproduced from the distal section and is propagated thereto via the skintissue.
 18. A blood pressure monitor according to claim 16, wherein saiddistal pulse sensor comprises a photoelectric pulse wave sensor whichemits a plurality of lights having different wavelengths toward thedistal section of the artery via a skin tissue above the distal section,and detects a photoelectric pulse wave representing respectiveintensities of said lights reflected from the distal section via theskin tissue or transmitted through the body portion.
 19. A bloodpressure monitor comprising: an inflatable cuff which is adapted to bewound around a body portion of a living subject to press said bodyportion through which an artery of the subject extends; a blood pressuremeasuring device which measures a blood pressure of the subject bychanging a pressure in said cuff; a pressure pulse wave sensor which isadapted to be pressed against a distal section of said artery located ona distal side of said cuff wound around said body portion, so as todetect a pressure pulse wave which is produced from said distal sectionof the artery and is propagated thereto via a skin tissue above saiddistal section; relationship determining means for determining arelationship between blood pressure and magnitude of pressure pulsewave, based on the blood pressure measured by said blood pressuremeasuring device and a magnitude of the pressure pulse wave detected bysaid pressure pulse wave sensor; blood pressure determining means fordetermining at least a diastolic blood pressure of the subject accordingto the determined relationship based on a magnitude of a lower-peakpoint of each of successive first heartbeat-synchronous pulses of saidpressure pulse wave detected by said pressure pulse wave sensor;cuff-pressure increasing means for increasing said pressure of said cuffat a predetermined rate; a cuff pulse wave sensor which detects a cuffpulse wave which is a pressure oscillation produced in said cuff; firstpeak-interval determining means for determining a first interval betweenan upper-peak point and a lower-peak point of each of firstheartbeat-synchronous pulses of said distal pulse wave which aredetected by said distal pulse wave sensor when said pressure of saidcuff is increased at said predetermined rate by said cuff-pressureincreasing means; second peak-interval determining means for determininga second interval between an upper-peak point and a lower-peak point ofeach of second heartbeat-synchronous pulses of said cuff pulse wavewhich are detected by said cuff pulse wave sensor when said pressure ofsaid cuff is increased at said predetermined rate by said cuff-pressureincreasing means; difference determining means for determining adifference between the first interval of said each of said firstheartbeat-synchronous pulses and the second interval of a correspondingone of said second heartbeat-synchronous pulses; and judging means forjudging whether said determined relationship is accurate, based on atleast one diastolic blood pressure determined by said blood pressuredetermining means and a pressure of said cuff corresponding to a timewhen the differences determined by said difference determining meanssignificantly largely change.
 20. A blood pressure monitor according toclaim 19, further comprising a control device which controls, when saidjudging means makes a negative judgment, said blood pressure measuringmeans to measure another blood pressure of the subject, controls saidpulse wave sensor to detect another magnitude of said pressure pulsewave sensor, and controls said relationship determining means todetermine another relationship between blood pressure and magnitude ofpressure pulse wave, based on said another blood pressure measured bysaid blood pressure measuring device and said another magnitude of thepressure pulse wave detected by said pressure pulse wave sensor.